Hi mattress shopper,
This seems to be a day for questions about heated blankets or mattress pads 
My reply in post #2 here would be the same for your question as well if the gel foam you are mentioning is gel memory foam. Gel can be added to any type of foam so if it’s another type of gel foam that isn’t heat sensitive then it would be fine.
The pad itself may also interfere with the ability of the memory foam to soften with body heat and contour to your body when it is turned off.
If you do use it with memory foam (gel or otherwise) I would use the lowest settings and for shorter periods of time.
Phoenix