I downloaded the RC3 on February 28 and installed it to address a couple issues we were having, then saw on March 1 that 10.1.2 was officially out. I downloaded it and went to upgrade, and it stated that it was already installed, but gave me the option of repairing the install.
Can I assume from this that 10.1.2 RC3 and 10.1.2 are the same and I don't need to upgrade to 10.1.2?
Yes, RC3 ended up being the GA build. So you are in essence on GA for 10.1.2