Nixif:
Well, technically it is kinda a verb. but the word of the spell says it makes grease and thats where the conflict is bred from.
But the grease spell itself clears up that problem with its own description, when it says clearly that it is not flammable.
So spell level 1 "grease" is NOT flammable
Spell level 2 "incindiary slime" is like grease but IS flammable and it can be found in Complete Mage of 108.