I have come across retreads while looking for Winter Tyres. There doesn't seem to be anyone shouting from the rooftops "DON'T USE THEM" but from what I've read their ability (in any and all situations) compared to premium tyres is a bit reduced but TBH you'd expect that for the price. I'm seriously looking at getting some as I won't be putting them through the same torture as my summer tyres anyway.
Nor sure of the truth in it but according to an article on Wiki' all retreads are tested according to the same load and speed criteria as those undergone by new tires.