The FAA rulemaking process on "drones" (I prefer UAVs) for commercial use has only just started. I took a peek at their initial proposals and I thought I saw that they were proposing VFR daylight only operation. That would cramp the style of anybody using them for a surveillance business, and would probably render any evidence collected that way inadmissible in court.Can drones fly at night? Can pictures be sent out?
Which, of course, is bat-poop crazy. Obviously you could do IR and thermal imagery surveillance with these things ... the military and police have done it for decades.
Personally, I'd go with game cameras. They're cheap, automatic, easy to set up, and perfectly legal.