I'm amazed that the frames that come in with the box store bikes (Excluding rusted frames) are "useless" except for recycling... Unless you are getting enough money from the recycling to keep the co-op running.
For a co-op, a frame is a frame. You can always put parts onto it. I'd hazard, by and large for those getting a bike from a coop, the frame is the least of concern (Assuming not rusted to high hell).