cavortingcheetah,
Normally not a problem. However.....
Emergency recoveries from Dive Boats are normally
Heli ops.
Unfortunatly there's a few of them in the summer around
the UK.
Normally flight limited to below 1000'.
That said with an exant casualty getting them into the chamber
is priority!
Dependant on how far you're looking at a good Rigid Inflatable (RIB)
with a honking great engine is fine for anything up to an hour or so.
Dive Eclipse - Recreational diving from Selsey, West Sussex
Whilst the differential up to the 1000' isn't that great there's
still a risk.
So short answer, possible but does pose an element of risk!
Some operatord in Autralia are offering Heli diving in the same spirit
of Heli skiing, but state, the max alt is limited to 500'.
HTH
DaveA