Infrared cameras can't see through walls or ceilings (unless you have your grow room in a poorly insulated attic with tons of really hot lights). Anyone who tries to tell you different is seriously deluding themselves.
What they're looking for is hot air being vented out of a house from somewhere other than a dryer vent, so the obvious thing to do would be vent your hot air into another room, the crawlspace, or the dryer vent.
While technically they are supposed to have a warrant to do an infrared flyover, we all know that there are cops who don't play by the rules. Once they've seen the air venting out of your house, then they'll check with the electricity company to see if you're using substantially more juice than your neighbors. THEN they'll get a warrant and say that the electricity company tipped them off.
Pretty shady, if you ask me, but that's law enforcement for you.
Someone on another thread made a good point about flyovers and budget restraints. Most states are in such bad shape they're cutting back on just about everything this year, so maybe infrared flyovers will be on the chopping block, as well.