Dave,
Does the on board vocalizer on your Korg work independently of the rhythms engaged, as when you're playing guitar, or do the styles have to be playing?
Sparky, nope. When I play guitar, or banjo I call up a user preset that is designed to harmonize in a selected key. TC gives you 3 options each for major and minor scales, so you can get the right "smart singers" to follow you.
For example, a diatonic scale has a minor ii chord, but some songs use a maj II, so you have to be prepared for that. Most often I use a standard diatonic scale harmony with a single third above my voice. When I'm on guitar, a simpler harmony sounds more realistic. When I'm in full KB mode, I can do more with multiple voices.