From the skill tree description (Bold emphasis added):
Superheated Rail – Rail shot Ignores 30% of the targets armor. In addition, if rail shot hits a burning target, it has a 100% chance to vent 8 heat and refresh the duration of your combustible gas cylinder’s burn effect if present.
So the way I read that is, regardless of whether or not you have IGC, CGC or IM running you still get the 30% bonus, but you only get the other two effects with CGC or IM.