If they use dummy heads (2wire) then yes you can use an external flasher. You have to rewire the bar. But I made a custom bar for my Xterra using dummy heads and hooking it up to CanTrol. Works flawlessly and allows sync to other lights
So the answer is yes as described above. The three wire modules I have work fine with a separate positive flasher. I'm going to use a ULF-44 to get the patterns and sync that I want.