How do you feel about headcanon of Dewey being aroace?
It fits.
Like- really fits.
In the Nightmare on Killmotor Hill episode, Dewey expressed being uncomfortable about a love interest, and it was the way he said and showed it that told me it wasn't simply the look of the... thing, nor the gender. Dewey seems like he simply feels uncomfortable with the entire idea of a relationship, and it makes sense seeing as it doesn't really fit his personality or lifestyle choices and expectations.
So yeah, Dewey being aroace seems pretty canon- at least to me.
And this could also just be me relating in some ways, but I think Huey is much the same as well. While Red is more romantic at heart and finds romance something sweet and in need of being celebrated, it seems like he might be asexual(possibly also aromantic but that still seems like an open thing for him).
Again, this is just my opinion, but the two seem this way to me.
Louie on the other hand? I can see Louie being much more open to the idea. Currently not now, but it seems like he's more in the childish "eww gross kissy mushy stuff yuck" kinda phase, rather then how Dewey actually feels intimidated by the thought of being in any form of a relationship, and Huey seems romantic for others but rather indifferent at the idea of being in a relationship of his own.
I plan to have Louie in an OC relationship in a future fic, but putting that aside, I can see him being more open then his brothers.
So to get back to your original question: In my mind, Dewey is completely Aroace and I really can't be persuaded to believe otherwise. :)