Man, what the fuck are they doing over at Gumroad? I wonder what site will be banning NSFW next.
I haven't seen others using Itch for anything other than games and (rarely) comics, but I also don't really search for much other than games. I don't see a reason not to use Itch as a way to distribute your art in packs; you already seem to be mostly using this for NSFW comics, so it's not like it would be a big departure, if that's what you're worried about. If it turns out to not be allowed per site rules, you could probably still make occasional posts promoting your stuff, so long as you're also working on games/comics/whatever is allowed.