The school where I did my IR had an engine out allowance which was to be added to the value of the published DA. This was published in the schools operations manual, and in the case of the seneca was 100 feet.
Go around on precision approaches are INITIATED at DA, and the aircraft WILL sink below this during the go-around. Of course on non precision approaches you don't go below MDA.
As far as QFE goes, why do we continue with such nonsense? Most IR schools these days use QNH for approaches. The last thing you want to be doing on a go around is messing about setting QNH waiting for the examiner to fail the engine.
How about high altitude airports? Think you can set QFE at an airfield 4000 AMSL?