I think you'll find that lots of tourny players on here ref now and again at big events, as most teams end up doing at least one or two tournaments a year to raise money if nothing else.
You also get teamswho ref regularly e.g. SAD (Midland Masters), Unreal (doing the whole M25 series this year), Manchester Marshals (!) who do events like S2k, Tigers do internationals etc etc etc. Lots of teams are made up from site marshals who ref together e.g. Control Freaks from Ground Control, 6E Marshals from 6E at Witton Castle.
Then many teams that play Millenniums will ref one round a year (compulsory for Pro teams I gather this year), and one or two of the S2k events are "self marshalling" which means the teams playing have all their byes together and have to ref a field for that part of the day thus keeping the event costs down.
Individuals who are probably better known for reffing than playing who are on these boards include Russell Smith and Ralph, who are ultimates for S2k and M25 respectively.