Lots of guys are shooting hogs at night with IR rigs...so its not automatically illegal. Check the regs and have fun!!!
That is the catch, the local state regulations, which for Tennessee do not seem to be including legal hunting hours between 30 minutes after sundown and 30 minutes before sunrise with night vision or thermal optics.
Most states encourage hog elimination.
Most states do, but definitely NOT all states. Some states have imposed laws against shooting hogs on public lands, such as Missouri. Louisiana apparently doesn't allow hog hunting (or night hog hunting?) during deer season (not sure of the specs, but my buddy who lives there complains about this). Until just recently, hunting hogs at night required local game warden permission, which was not always granted and was property specific. Many or most states do not allow night hunting on public lands. Some states do require licenses for dealing with pests and some don't. One state makes you get hog tags if you want to shoot hogs. In other words, while states may encourage hog elimination, the legalities of compliance can vary widely from state to state.