Some people will absolutely disregard you.
Some won't. It's going to completely depend on your area and the people in it. I have fostered for 2 rescues that allowed me to have intact animals and they completely understood why and trusted that I wasn't some crazy backyard breeder. I was turned down by many others for the reason that they were intact.
There's a german shepherd rescue a town over that I work with and donate a lot to - I know the owner through GSDs/training - She is a breeder and rescues as well, so someone like her would have no problem letting a dog/litter be placed with a responsible owner of intact dogs. I love her program and really admire her- They adopt out about 10 GSDs a month and transport many all the way from california. She runs a boarding kennel and keeps all of the dogs right at her place in the kennels while they get out for a lot of training, play time with each other, and socialization. The best part is since she's really involved in the dog breeding/training world, she's very knowledgable and places dogs very well. I only know of one dog that has been returned to her and judging by the owners he was adopted to, it was not her fault for his poor placement- it was their wishy washy attitude towards rehoming dogs.
Good luck finding a good place to work with - and don't get discouraged if some turn you down. If they're that uneducated and biased, you probably don't want to volunteer with them anyway.