Apart from the fact that Tesla simply wouldn't want to give a competitor a leg up like that, and GM wouldn't want to commit to a non-standard charging spec/adapter...
Ultra-high charge rates simply don't make sense for an EREV like the Volt. First of all, it's not needed for utility. (You can already drive long distances quickly and conveniently on gas.) And, second, with a smaller battery pack, a Volt's battery cells wouldn't be able to handle the high amounts of power that a 60 or 85 kWh battery pack could have without degrading the cells.
However, for the much-anticipated and as-of-yet unnamed 200 mile EV that GM is rumored to be making, quick charging capability could be a huge deal. But, still, I agree with telveer, that it would be better if "we" could get started on a rival network of quick chargers that would be non-proprietary and open to anyone, rather than try to piggy-back on Tesla's proprietary system. But without the proper incentives, such a network may be very slow to develop. So I worry it may not happen for a long time.