Right I always thought that hot water was for undergarments for sanitary reasons but apparently "hot water" is about 140F which does absolutely nothing in that sense. And as far as pollens and allergens, a long rinse cycle apparently is much more beneficial than that 140F temperature (which again isn't anywhere near boiling). Also a front loading washer is better because in a top loading one the clothes "sit in a stew" of the dirt for a long while and then they get a brief rinse. With a side loading washer, the water flops around through the clothes, the dirt gets away from the clothes right away, and the allergens are flushed out and don't sit on the clothes. But the long rinse is really important to get all the detergents and other allergens out of the clothes at the end.
I think with the oils for poison ivy and poison oak it is the detergent that matters, not the temperature. You want a detergent that lifts the oil away from the clothes and gets it out in the drain so again a long rinse cycle would be critical there. Otherwise the washing machine, if you had a top loader with little rinse, would just make sure all clothes in the wash were evenly coated with the oil