I have used a FLIR on a few occasions to find suspects who fled into a wooded area and laid down. I agree it can be dangerous to focus on the FLIR and not your surroundings.
One person runs the dog, one with a FLIR and two cover officers is ideal, especially in a high risk fleeing case.
One time the dog kept running circles in a particular area, but we never located the suspect. I waited on the FLIR for an hour while we maintained the permiter. The FLIR showed his heat signature, and I found him dug in, buried himself under three feet of dirt, leaves, and sticks with an air hole for him breathe out of.