According to Don Rosa, he is!
Don Rosa described Daisy as the sister of Donald’s brother-in-law, so Della’s husband and the father of Huey, Dewey, and Louie is/was Daisy Duck’s brother.
So far, Huey, Dewey, and Louie’s father has never been given a first name. His last name is only listed as “Duck,” in the Carl Barks and Don Rosa family trees.
Don Rosa explained that the surname “Duck,” is very common and the equivalent of “Smith.” All the same, it would still be quite the coincidence for both Donald and Della to fall in love with people with the last name Duck… but less so if their loves were related to each other.
When I learned that HDL’s father and Daisy could be related and asked the good people of DuckTalks if they’d ever covered that topic as a possibility for DuckTales 2017, Infinirama said he had early on, back on October 20th, 2017 (his post can be viewed here). Nevertheless, he’s given me his blessing to bring this matter to the fandom’s attention once again.
Frank Angones has said on Tumblr that he and the Ducktales 2017 crew are very familiar with the Duck family tree, and that they are primarily working from Don Rosa’s family tree for the show.
We also know Daisy is set to make an appearance. Frank has answered several questions on Tumblr from fans wondering if Daisy will be in the show. He answered one by saying, “spoilers,” and at least four with “Please see pinned tweet.”
In June 2018, he also answered another question from a fan and explained some of their early plans for Daisy and why they decided to scrap those plans.
Then last March, we got a hint that they may have figured out who they want their Daisy to be:
This could mean that Daisy is set to appear either toward the end of Season 2, or sometime during Season 3.
What’s interesting is that if the DT17 crew are sticking to Don Rosa’s account of the Duck family, then Daisy might truly be Huey, Dewey, and Louie’s aunt on their father’s side in the show. And if that’s the case, we can expect her appearance to shed some light on HDL’s father’s identity, whereabouts, and/or fate.
Now that Della is home, many fans are expecting some little hint about the father – any tiny bit of information that could possibly indicate that HDL’s eggs weren’t just dropped off by a stork on the doorstep of McDuck Manor one morning with a note that said: “To Della Duck.”
After all, when asked about HDL’s father last June, Frank did say “one parental mystery at a time.”
With the Della mystery nearly wrapped up, it may almost be time to move on to the next parental mystery!
DuckTalks 
What do you mean “nearly” wrapped? She’s back on Earth.
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Excellent question! I say “nearly,” because we still don’t have all the information about why Della originally took the Spear of Selene. That’s still a mystery. All we have is Scrooge’s idea that she took it on a whim, but that doesn’t explain why she left a note saying she was sorry, or why she bothered to leave a note at all. It also doesn’t seem to be in her character.
Over and over again, the show has had characters accusing Della of not thinking things through and being reckless, and then proving that she did know what she was doing all along – everything from bringing extra food and a large tent when she went looking for Santa, to the way she flies the Sunchaser/Cloudslayer, to thinking ahead of how she’d make it out of the seed vault.
We also saw Scrooge get frustrated with Della in “Raiders of the Doomsday Vault!” because he has a lot of unresolved anger and hurt over the Spear of Selene incident. He never brought up the rocket when he yelled at her, though. That issue is still unresolved. And I can imagine it’s going to come back later on, and he’s finally going to accuse her to her face of taking the rocket on a whim and not thinking about the damage she caused. Now if Scrooge’s side of things were all there was to it, all Della could do at that point would be to sincerely apologize… but she’s already done that twice, so in terms of storytelling, it’d be writing in circles and anti-climactic. If, however, there is another angle to the story we haven’t heard yet, that’d be a fabulous time for Della to say, “You think I took the rocket for fun?!” and deliver a vindicating twist.
My Tumblr bestie alliterative-albatross and I have our theories as to Della’s reason for taking the SoS (the main theory being my bestie’s idea). Links to our ramblings can be found here, if you fancy some conspiracy theories: https://drummergirl231-2.tumblr.com/post/182989569965/i-support-della-duck-masterpost
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Well nothing was brought up about some ulterior motive…so looks like she took it for the wrong reasons.
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I’m sure you’ve noticed of course that Della hasn’t talked about her original reason for taking the SoS, and there’s nothing wrong with writers dragging things out over three seasons. She’s apologized for ever stepping foot on the rocket, but that doesn’t mean her original intentions when she stepped foot on the rocket were “the wrong reasons.” It just means she made a mistake somewhere along the line. Was she investigating a possible sabotage only to set off the launch sequence, leaving her only enough time to scribble a note, get back on the rocket, and blast off so it wouldn’t crash in a populated area? Or did she pull a Donald and more or less do the same thing only instead of investigating a conspiracy she was just checking out her present when she set off the launch sequence? (The original launch sequence would’ve had to have a longer countdown than the reassembled Spear, of course). Innocent motives, utter mistakes that would lead her to regret. These seem to be far more in-character for this unlucky ducky than less charitable fan theories. Also, do remember that Frank and the team would not include HDL’s mother in animation for the first time to make her a baby abandoner that fans were supposed to hate. Finally, each season has focused on a particular triplet and drawn strong parallels between them and their mother, especially with regards to the SoS incident. Huey’s season is up next and according to Frank he’ll get wrapped up in F.O.W.L. conspiracy theories. With the reveal of Scrooge’s board being evil (as alliterative-albatross predicted), the theory Della suspected sabotage is not too far out there, and her parallel with Huey could be that when you look for trouble, you find it.
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