Doesn't really make him a role model IMO with the exception of fighting evil with a wand. Not terribly realistic though.
I don't have issue with a gay charachter in a book or play, the issue is that parents now may be "forced" to address sexual orientation with their kids before the child may be ready for it, and who gives anyone that right to make that decision for a parent? There are kids yet who haven't heard, and eventually they will hear it from another kid at school.
My point was that most of the people you listed are dead, or so old and reclusive I thought they were dead, and pretty much unknown to the average middle school child. You don't have multiple blockbuster movies featuring Bruce Hayes (Warhol was in an Austin Powers though) and while Vidal is a prolific writer, his books & essays are not standard fare for kids like the 7 Potter books.
As far as a gay Dumbledore forcing a parent to discuss sexual orientation with their child, I guarantee that they already go to school with a child who has a gay parent, relative, or family friend, listen to music by a gay artist, and are constantly hearing
much worse things than "Dumbledore is gay" from their classmates and the media.