All I can say to this, is that if you can tell they are not homophobic or an asshole, worst us straight guys are going to do is say no, and I'm speaking from experience of being asked out by some of my friends who are gay, and a couple of them I only became friends with after being asked out. It's really flattering, because most gay men have alot higher standards than women, and it acts as a huge ego boost to us. So as long as you know that they won't get pissy or violent with you for it go for it. Or don't cuz I'm just a random stranger on the internet. It's really your perogative!