Maybe. Depends on which walll oven and which cooktop. You have to read the specs and understand cabinet construction. Generally, most manufactureres will tell you if their units are compatible. But no one will ever tell you that it's OK to mix brands. You're on your own on doing that math.

I recently replaced a 6-year old Electrolux induction cooktop which was installed over a wall oven. I thought the premature failure of the cooktop might have been caused by heat from the oven. When I pulled the oven (required to get the cooktop out) I found the original installation instructions for the oven still taped to the top of the oven inside a plastic envelope. Neither the paper nor the plastic envelope showed any signs of being exposed to heat. From this I have concluded that heat from the oven did not cause my cooktop to fail . . . and that there should be no problem installing a cooktop over a wall oven if the clearance required by the cooktop manufacturer is maintained.