Yes and no.
“DC offset” typically refers to a static amount of shift in a signal, which is undesirable because it’s constant and will interfere with the signals, limit your headroom, etc. But when you feed the DC offset into a RingMod, you’re actually turning it into an oscilator. It’s no longer a static offset at that point, since it’s being modulated by the RingMod effect, and you’ve transformed it into an evolving waveform instead.
Take a look at a demo I posted recently which takes advantage of a similar technique:
Renoise Native Monophonic Synthesiser 
I was going to suggest this earlier, but I wasn’t sure if it would be suitable for you. If you do this, then you’re really just synthesising your own new sounds, and you can of course tune them any way you want to. You only have a sine, triangle, sawtooth, squarewave, etc., to work with, but if you are comfortable with designing synth patches then it’s not that difficult to turn these basic waveforms into a nice instrument, which you could then use for microtonal music.
So, the RingMod is nice to use for this purpose, but I don’t think it’s really suitable as a method of tuning existing sounds.