Hmmmm, maybe. Terminology changes over time, however, so while in the misty beginnings of fanfic, slash = non-canon relationships, that is not what it is generally accepted to mean *now*. I'm in HP fandom, so by your definition, Draco/Hermione, Harry/Hermione, Dumbledore/McGonagall, Remus/Sirius are *all* slash pairings. For that matter, Ron/Hermione would fall under the same definition, despite the fact that they are likely to become a canon pairing in the future. I think if you tried that one out in this fandom, you would meet some hardcore resistance from slashers and het fans alike.

Perhaps the term "slash" has become synonymous with "gay" but I fail to see exactly what is wrong with that. It's a term that is widely recognized as defining a same-sex relationship within fanfic and I honestly don't think most fans see it as something negative. The subversiveness (or not) of the subject matter has little to do with the word describing it. You could call it "flibbertygibbet" and if the reader/writer perceives it as subversive (or not), then that's what it will mean to them.

Besides, slash is more acceptable in terms of labeling fic than calling it "gay" or "homo" as opposed to "straight" or "het".