Studies have shown that Games don't really benefit from being on an SSD, except WoW.
Programs may not load faster if the OS isn't also installed on the SSD, as the *.dll files will still be on the drive with the OS, and not load faster.
Seriously, why wouldn't you install the OS on a SSD? Once you go SSD, you'll never go back!
But to answer your OP, NO. You could use it as a second drive.
And if it's a second drive, WIE will NOT regonize it. In WEI, it states primary drive only.