I looked at half a dozen listings and none of them had any detailed information. It's impossible to determine from that what their behaviour will be. I would *assume* that they will have a default sequence/flashing in the absence of a PWM signal from the receiver, but the only way to know will be to test them. About 12 years ago I built an F1 safety car and used a police light bar on the roof, but it was "dumb" in that it only have wires for power. It did have a separate button to press for alternate light patterns.

If they absolutely required a PWM input, and space wasn't too much of an issue, I'd buy a cheap servo tester (~$6), strip it down and hook that up.