rushing

Are you at a large disadvantage if you don't participate in this?

no, it's not necessary, but if you did a good job during dirty rush it can definitely help your chances

"most houses keep an open mind" Which ones don"t?

The only houses you should really be worried about regarding dirty rush are the top ones. Like very top. Almost all the other ones take at least some guys from rush week. You should definitely be fine with mid tier houses like Chi Psi and Llenroc, although do keep your options open for the first round of smokers and don't be afraid to check out "lower" and "higher" houses too to get a feel.

What if you know a couple of the guys but haven't been to dirty rush events of a "top house" (this would be a very top house) though

Lol that literally means nothing. Most people know someone in top tier frats, but yet only a couple hundred guys are in those organizations. Unless you're legitimately good friends with these people, simply having their contact does not mean you have any better chance of getting a bid than the next guy. You need to take initiative to get into top frats, so don't rely on simply knowing a couple dudes to do that.

i just got to know some guys kinda well at a selective house, but i think its too late to be invited to dirty rush for the rest of the semester. Should i still be optimistic?

The large majority of fraternity members are outgoing and sociable. For that reason you have to realize that among the hundreds of brothers in selective houses, there are sure to be many many guys like you who they get to know kinda well through classes, clubs, events, etc. That being said, if they're not inviting you to rush events, or at least to their houses to meet more brothers and hangout (since many events have passed) then you shouldn't take your connections with them to indicate any increased likelihood of getting a bid. If they're not inviting you, its not necessarily a bad sign though. If they're not super involved with the house/rush then they wouldn't think to bring you around even if they would vote to bid you come rush week.

Make sure to cast a wide net of selective and less selective houses, but don't count yourself out of the more selective ones yet

i've been invited to hangout, just not an actual party :/

No house already has a PC. Of course AD, sig chi, and sig phi have guys in mind that they want in their pc, but nothing is ever set in stone. If you like the house, go during rush week. I know multiple guys who still got bids without dirty rushing

What about dx?

Pretty much every frat above the lower tier has guys in mind coming into rush week. However, legacies and very close friends aside, no one is guaranteed a bid based off dirty rush and no pc's are set in stone. If you're truly a good fit for the house, you'll get a bid regardless of whether you went to their dirty rush events or not.