Okay, I feel kind of embarrassed asking this question.
So I use Reaper and FL Studio on my PC, and Logic/Pro Tools on my Mac. However, I want to put Reaper on my Mac just for the heck of it. I have a lot of VST plugins for FL Studio and Reaper, but I guess it just never crossed my mind as to what kind of plugins Reaper would use on OS X. And before you even suggest it, NO I'M NOT BOOTCAMPING.
So, like...do I need "different" versions of my VSTs for Mac?
Yes, you'll need Mac versions of the plug. If you have windows version, Mac version it's usually included in the purchase. If you have an Intel Mac, the mac version should be UB (Universal Binary). Go to the developer web and check it.