I have used wifi tether on my GN with my unlimited data plan on AT&T. It works great. As for if you will get caught or not, that is an unknown. There are several people on the forums around here and elsewhere that have gotten the dirty letter and text message from AT&T telling them to knock off the tethering. I have been doing it for a few years now, I had a Nexus one on AT&T, then an Inspire 4G rooted and running Cyanogen Mod with the wifi enabled, now the GN. I have never received the dirty letter.
I am of the impression that heavy use will flag you, I really don't use tons of data. I abuse my phone, but I spend most of my day on wifi and only use the hotspot when I am somewhere without free wifi, or with crummy free wifi (I have found far too many Starbucks that speed test under 1MB down).
There are also those around the forums that will absolutely flame you for suggesting that you use your hotspot because it is against the terms of your contract and thereby you are committing petty theft. To that I say... I would love to give AT&T another $20 per month for this service but I will not give up my unlimited data to do it. (On another subject it seems that people are starting to see data throttling at as low as 2GB per month so be warned about that if you plan on tethering much.)