I have a MacBook Pro w/ Retina (2012 I believe) which has a firmware password which I don't know. Since it is a retina I can't use the remove RAM trick. If I go to reformat and reinstall the MBP will the firmware password be removed?
Your only option is to visit an Apple Authorized Service Provider (AASP) or one of their Genius Bars. The process to bypass a firmware lock changed a few years ago and now requires that a certified technician (ACMT) contact Apple with the Mac's information, which Apple will then process and use to remove the firmware lock.
You can find a list of AASPs using Apple's locate tool, https://locate.apple.com. Select the service option and search for a provider in your location.
Even with older Macs, where the firmware password could be bypassed by changing the RAM configuration and resetting the PRAM, the firmware lock would persist after wiping the hard drive and re-installing the OS. This behavior still exists today.
No, the firmware password is hardware specific, it has nothing to do with the installed operating system. Also, Apple may be hesitant to assist you in removing it. Situations where someone has a laptop which is locked out with a firmware password which they don't know is frequently indicative of a lost/stolen laptop. Imagine if you lost your laptop which had a firmware password, how would you feel about the thief being helped out by Apple?