Depending on the CHE and the dome/fixture the dome can trap heat and could lead to damage to the bulb or the fixture (socket or wiring). I guess just be mindful of the temperature it's getting.
Heat mats are pretty lousy for ambient temps, they are conductive heat mostly so they heat up wha they touch and little else. That said I dont have a problem with the heat may in either roach tank - they just cluster up where Ty want to be.