Just an update...
I looked at my VZW call log and the call I made on my ObiApp using only WiFi *did* show up and get counted against my cell phone minutes.
I don't know why that is, but that 1 minute call was listed and added into the total for the month.
So I guess the answer is YES, at least on Verizon if you use the ObiTalk app to make a call, even over WiFi, the cell carrier will count those minutes.