It's impossible for guerrillas to hide from FLIR etc if the rulers don't care about collateral damage (think Chechnya).
But policing by free-fire zone tends to also solve the G's recruiting problems.
And a sufficiently nasty guerrilla can do some nasty things...like, for instance, infiltrate LA on a hot summer night, steal a police cruiser and a uniform, and then shoot at a crowd of different-ethnicity folks for no discernable reason, then retire at high speed to an enclave of like ethnicity and watch the riots get started...
Hell, all you'd REALLY need in some cases is a rumor of "police brutality," and the riot starts.