Yes, Mach3 can do polar coordinates using G16, but while in that mode it can ONLY handle G0 and G1.
Unfortunately the manual promptly shows code using G83, which violates the restriction and DOES NOT WORK - at least with V.062. This is due to how Mach3 handles default values and polar mode. It's a bug in a way, but a very esoteric bug.
I did not understand your question #2 - sorry.
Cheers
Roger