But the same situation would occur if the Safety Pilot was incapacitated ....
Maybe so...
However, you are looking at in an increased risk, however small, which does not appear to be covered by the current published CAA criteria.
As I said, the correct course of action is to ask for an opinion from the CAA as to whether it is permitted to have two pilots flying together who both require safety pilots.
Only they, not an Insurance company, can give you the definitive answer.