Setting Priorities
O(riginal) P(oster), do you mean that for an approach, where GPS is a requirement, you think that you should disable DME/DME updates, in order to be legal?
Isn't the priority sequence for updating, first GPS position, then DM/DME position, then VOR/DME position, which last mentined mode could be fighting for priotity with raw average INS position depending on time in NAV mode?
If GPS is available, IT will be the primary position source, so it wil not be necessary to DISABLE DME/DME updates. If DME/DME updating happens to be the primary mode, it means that GPS is not available, and if that is the case, a GPS REQUIRED approach cannot legally be performed.
Don't start your reasoning process from the back-end of the solution.