"I don't know much about raid setups and installing games in a raid setup vs installing games to a secondary hard drive. In raid do both drives act as the same drive letter?"
>> Yes, to the OS it's a single device.
"If I switch to raid will I need to re-install windows?"
>> Yes, the controller will have to initialize the drives, which will destroy the existing data.
I usually use a single SSD, or 2 SSD's in a RAID 1 for my OS, and setup 2 SSD's in RAID 0 for games. RAID 0 offers no redundancy (who cares, games can be re-installed), but reads/writes are much faster.