I know its a moot point - because the optional isn't going to be coded anyway - but is this one of those Axis fanboi rules or does it cater for the British midget subs too?
After Italy changed sides in 1943, the frogmen captured at Alexandria offered their services to the Royal Navy. The RN accepted and a joint action by Italian and British frogmen sunk two Italian heavy cruisers - by then in German hands - in La Spezia harbor. Should the rule be used it could be interesting to state that it is easier for the British to use frogmen if Italy falls.
I agree with peskpesk and Harry Rowland, the game designer himself, Frogmen can potentially achieve an effect in the Med war theater and can make games more variable and interesting. It would be really great, if this optional could still be coded.