That kind of dates way back... remember The Edd Zone (later renamed Edtropolis)? It was like the premiere EEE fansite there was on the web, even approved by Danny Antonucci himself, as well as number of the aka CARTOON personnel were aware of its existence; but it also a home for a number of fan works: fan art, fan fiction, fan poetry, etc. and OCs abounded (admittedly, I evented an EEE OC named Ted, who was a bespectacled dork that became like the unofficial fourth Ed since his name rhymed), but the webmistress did implement certain rules for OCs, such as fanfics were prohibited from becoming too focused on them, and a each OC had to appear in X amount of fanfics (in a supporting role) before they would be recognized on the site itself (which had an encyclopedic index of OCs)... in the fan art section, however, it wasn't too uncommon to see pics from artists of nothing but OCs, and like you say, sometimes they're not even in the EEE style, some were anime/manga style, some looked more like Disney/Bluth-esque designs... and yes, I seem to recall there being a thing about vampire hunters as well... in fact, I think one fan on that site had like this series that involved Double D having a dracula-esque counterpart.
I think the webmistress finally became bored and gave up the site altogether a few years back, I remember there being outcry because it was such a vast site (it'd be like if ToughPigs were shut down), but some people try to relive it through the Wayback Machine.
But I agree, that's always been one of my biggest problems when it comes to OCs and shippers, that was an issue I had even with the Chipmunk fandom, often times whenever an OC was created, it was usually a Munked version of the fan, who wanted to ship themselves with their favorite Chipmunk or Chipette (and no, I never Munked myself so I could pair myself with Jeanette), but even then, there were cases of some fans trying to ship their OC(s) with someone else's OC(s)... then again, THAT fandom has loads of problems with shipping in general, which is why I don't ship anymore myself, because flame wars between canon shippers and mixed shippers get utterly ridiculous.