My guess is there'd need to be more respect for fanfic among the older sf fans, but I could be wrong about that. I'm not the only person for whom HPMOR is the only fanfic I read. (I've read some other good fanfic, but I don't get around to fanfic generally speaking.)

I think a sufficiently high proportion of likely voters are on line, but this is based on a feeling of plausibility rather than actual knowledge.

When you talk about which award you're going for, is this just a matter of which award you encourage people to nominate it for?

In terms of prestige, I think you'd be much better off being nominated for Best Novel and losing than winning the Best Fan Writer award.

I find it hard to imagine you winning, but I also find it hard to imagine specific reasons that would make it extremely unlikely. It's quite possible that I'm just engaging in availability bias (all the other winners have been conventionally published) rather than anything more solid.