Sort of, yeah. Yaoi, by definition, is supposed to be actually pornographic as opposed to just romantic (which would be shonen-ai instead), but what the twins in Ouran did was a little more lewd in nature, so yeah, I'd call it that. Besides, people are using the term yaoi more and more broadly these days. Sometimes it doesn't mean pornographic at all...
Ouran Highschool as a great anime, for the record. I love it. :xd: