Macbook pro mid 2012: Can I install win 8.1 UEFI or will I have driver issues?
Any MacBook Pro with model identifier of MacBookPro10 or less does not have an UEFI. MacBook Pro (15 and 13 inch, Mid 2012) computers have model identifiers MacBookPro9,1 and MacBookPro9,3, respectively. The MacBook Pro (Retina, Mid 2012) has model identifier MacBookPro10,1. I assume your model does not have a Retina display, therefore I assume you should install using a BIOS/MBR booting.

I hear UEFI offers faster booting. I also hear this requires a single boot configuration. Well, you will being dual booting with OS X, so you can't take advantage of this feature anyway.

Another advantage to UEFI booting is access to a larger number of partitions. UEFI booting uses the GUID partitioning table (GPT). This has default limit of 128 partitions. BIOS booting requires Windows to use the MBR partitioning table. This limits Window access to only 4 partitions in  the GPT. On Mac computers, generally 3 partitions are used by OS X, leaving a single partition for Windows. There are ways around this single partition limit, but this requires abandoning the use of the Boot Camp Assistant.