A couple of years ago it became an issue with SAR helos getting refuels on rigs, only because the refuellers couldn't cope with basic safety strategies such as being cleared into and out of the disc by the rearcrew - they just did their own thing, wandering around the TR and running the hoses under the helo without clearance.
Fundamentally, as FED says, there is nothing intrinsically dangerous with rotors running refuels on rigs, either gravity or pressure refuels - just a small amount of training and professionalism required.