The gliding clubs which I belonged to all required their tug pilots to have at least Silver C gliding standard. Quite rightly so in my opinion. A non gliding tug pilot tends to give poor value for money, let alone lacking the situational awareness and anticipation of the movments of the non engined aricraft operating from the airfield.
I've done a bit of tugging and suffered quite a few missed heartbeats as a result. Personally, if I'm spending all day on a gliding airfield, I would rather fly the gliders. I left the tugging to those who enjoyed it more and those who were hours building.