I've never used the NuvaRing, but have used pills with the same type of hormones in, and have been charting since August 2011
The NuvaRing has the same hormones in it as the combined pill, so it will prevent ovulation. Therefore you will not get the same temp shift that you would if not on hormones, as you will not be ovulating. Your temps will stay pretty steady throughout your cycle, though they may change in the week that you have the ring out.
There's no harm in temping, it just won't show you anything useful about your cycle. But to get used to doing it, technique, forming the habit of temping first thing, etc, before doing it 'for real', sure
Though if you plan on temping for contraception before TTC and after stopping the ring, I'd recommend learning the Fertility Awareness Method, which takes in cervical mucus and various other things as well as temps.
While you're using it, the ring should regulate your cycles the same way as being on the combined pill would, as the bleeds you will get are not a 'real' AF, but a reaction to the withdrawal of hormones when you remove the ring. Your cycle may or may not stay the same after you stop using the ring. So it regulates, but it's an 'artificial' regulation, if that makes sense?
I hope that helps
