Can I use a guitar/bass tuner (GA-2) for a bowed string instument?
"Can" you? Sure. Since the GA-2 is optimized for guitar/bass and a viola is, well, neither guitar nor bass, a better option would be something more "universal", like the TM50 or OT120.
The Korg GA-2 will detect and accurately tune the notes for a violin, so yes, you can use it. It's optimized for guitar in the sense that it displays the string numbers as well as the notes (1E, 2B, 3G, etc) and those don't correspond to the same strings on a violin. If you already own a GA-2 for your guitar, it makes sense to use it. If you are buying a tuner specifically for violin, there are better choices. I would argue for a "chromatic" tuner which detects all notes like the Korg CA-1, or better still a clip-on like a Snark SN-1X.
You can get a free tuner app on your phone, too.