Serving as assistant to Diagnosan Tocot, Grunshlik has other priorities and deals dangerously - yet argues with Tocot that he's invaluable to his work.
At the medical centre, Grunshlik's primary duties seem to be negotiating (rather persuasively) with customers, and helping out around Tocot when he performs operations, though he admits he can't stand blood. It's not really known whether Grunshlik inflates the prices of Tocot's services so he can take a share, but it's quite probable that he does.
When it was found that Scorpius had his cooling apparatus fitted by Tocot, the Scarrens made a deal with Grunshlik to leave a spy at the medical centre, frozen as a donor. However, Grunshlik hoped to play the Scarrens against the Peacekeepers, and sent a message to Scorpius when Crichton arrived. This way, no matter which side came out on top, he'd hopefully get some sort of reward.
Unfortunately, his reward was to have his body remote-controlled by a neural interface with Scorpius, and then to be frozen as a donor himself by the Scarren spy. Not an entirely sensible move.