I believe there is a rule within the BGA comewhere that talks about 'combined experience' of 6 tows. This means that the glider pilot must have completed 6 solo tows if the tug pilot is on his first solo, and vice versa.
As a glider pilot and power pilot, I would say with my gliding hat on that I wouldn't want to be towed by a non glider pilot. Gliders can be very slippy and a tug pilot suddenly throttling back or decending for some reason can be very uncomfortable (as you pull along side the tug with a big bow in the rope.)
On a non safety aspect, glider pilots tend to read the weather and clouds a little better than most power pilots, and the turbulence caused by cumulus that most power pilots would avoid is exactly where the glider pilot wants to be dumped. When you pay £20+ for an aerotow, you want to be dropped in the best available lift in the sky!
TBK