Whether or not its been done safely for years in other countries, in the UK if you refer to CAP 748 - Aircraft Fuelling and Fuel Installation Management it states:
3.2 The fuelling of helicopters with engines or rotors running should be prohibited when
fuelling with:
a) gasoline or with wide-cut turbine fuels not containing an antistatic additive; or
b) kerosene or wide-cut turbine fuels containing an antistatic additive if the fuel inlet
is positioned so that the exhaust system is at the same height or lower, or if it is
on the same side of the helicopter.
If I was the aerodrome licencee/owner I would have jumped all over that crew.
Biz