Well, today I watched 5 RYR aircrafts on the tarmac and I didnīt see any soul comming from the cockpit to check the fuelling. Actually in two of them pax leaving were waiting on the bus to be boarded meanwhile pax arriving were boarded on different buses.
The refuelling supervisor does not have to "come from the cockpit" - it could be a ground engineer, for example. Normally the way to communicate would be via a headset plugged in outside to the interphone but an open cockpit window with said RFS banging on the nose and shouting to attract attention may arguably satisfy the requirement (not saying I liked that system myself).
Are you sure refuelling was actually taking place
with passengers on board? Just because the bowser is connected does not mean that fuel is being pumped.
If crews are disobeying this regulation then they do so at their own peril since this aspect is monitored by SAFA inspectors and also Company personnel. Also as Captain I wouldn't like to be held liable in the case of fire and loss of life/injury.
As has been pointed out previously Ryanair are, to my knowledge, the only airline that requires crews to nominate a Refuelling Supervisor.