Keep in mind the heat cable can still be within it's specifications and have leakage high enough to trip class A GFCI device. Longer the cable run the higher that risk is, you possibly have short enough runs it is not an issue. I have used class A GFCI on many condensate drain heat cables, many only being 10 feet or less and never had nuisance trip trouble with them either.FWLIW, a friend of mine has a half dozen of these, plugged into conventional GFCI receptacles, and with no problems from nuisance tripping.
I agree with what you have said. exception in 210.8 says "Exception to (3): Receptacles that are not readily accessible and are supplied by a branch circuit dedicated to electric snow-melting, deicing, or pipeline and vessel heating equipment"Oh ok. I don't have my book handy, the question is is there a location requirement for the 426 GFPE? Does the branch circuit require GFPE or just the heating cable?