I have my GTP, BRB and Bloods in the same room(all similar needs). I heat it with a oil filled heater set to 80. I do also have rhp's in the cage for a warm spot but the spots are rarely used. I live by"one is none" and try to have a redundant system whenever possible. This is easier for me though since I'm not a big breeder. Heating the room alone is good but like many have mentioned have another heat source available just in case you need it. Better to have it and not need it then need it and not have it.

Also on a side note:
Before I got my pvc cages I kept my blood in a tub with just the room heater and she was doing great.