radSS, I agree that what you propose is perfectly code compliant.
Regardless of what you are installing the code requires a disconnect that "shall" disconnect all the ungrounded conductors, that in no way prevents you from disconnecting all the conductors at the same time.
As a matter of fact the disconnection of the grounded conductor is actually required when dealing with fuel pumps. 2002 514.11(A)
In your case I do not see the need to disconnect the grounded conductor but you certainly can if you want.
If this heat trace was cord and plug connected the grounded and grounding conductors are all disconnected simultaneously, doing the same with a switch is fine.
Bob
