After the models agent wrote to gran saying she couldn't go Nathan choose Tim to take her place at the party, I think Dan did call Tim a fag at this point but choose to invite hime for Nathan.
At the start it was stated that Dan is a surfer (connection to Blake) and Natahn is a skater, which would explain why he likes Tim, not nessesarily because he is gay (his wall of ledgends is two walls full of half naked women, his computer is packed with porn that Dan catches him wanking to loads [Which is a bit to much effort to go to just to cover up being gay])
If either of the boys did turn out to be gay I would suggest it would be Daniel rather than Nathan. A few of his scenes he has given off a kind of gay vibe and at one point I thought this was one of the reveals Chris was building up too. may just be a coincidence or it could even be a diversion to throw previous Chris Lilley fans off the scent (since most of us know his formula of comedy by now)