This is only a plothole if we start from the assumption that Rusty is the one behind some of the shady business(drug trafficking) around the college.
Another explanation could be that Tommy offered acess to the house and its members for Quinn in exchange for some fix, since he is likely a junkie.
That would be a nice boost to her prostitution business and possibly better than trying to pimp girls via bathroom stalls or to the Jocks who seem to have several sexual issues thanks to their abuse of steroids.
About Rusty and Tybalt, they couldn't be more different. Rusty is a party animal who enjoys loud music, cheap beverages and strippers, meanwhile Tybalt likes expensive drinks and suits and his idea of fun is making plegdes for the Alpha&Omega suck lemons.
So maybe Rusty isn't there because he simply wouldn't fit among people like Tybalt.
I still got the feeling the one behind the drugs is a teacher with some oversight power over the academic body and the faculty staff. That would ensure a better protection from prying eyes: make the students to sell the drugs while you use your power to make sure no suspicious leak to outsiders.