I read somewhere that the hipppies were supposed to have driven/crashed their van into the river ( presumably in a spliff-fuelled haze) and Jack and Ennis were shown helping to get them out. The rationale at the time was apparently to make them appear heroic/male/whatever - real men pull hippies out of rivers? I suppose it might have made an intersting contrast with Ennis's resctions to the bikers - yeah, I know bikers and hippies are two different things.
Why this scene would have been so disastrous, I think, if that it would have introduced extraneous charcters for no real reason and would have shown the outside world intruding on that of Brokeback, and undermined the efect of Aguirre's arrival/intrusion.