Boy with overprotective mom

My son has a boy in his class with a very protective mom.  Basically every time the boy has a conflict with another kid or gets hurt (even if just accidentally during playtime) she insists that her boy is a victim and the other kid is hurting her kid (the word bullying is thrown around a lot too!!!) and that the other kid needs to be separated from her son and not play with him.  The teachers are going along with it.  My son told me this week that this boy has nobody to play with during recess -- at this point the list of kids who are not allowed to play with him is over half of the class and includes most of the boys (I believe all except for 4 boys).  My son was added to the list a few months ago because the other boy fell and skinned his knee during a game of chase and tag at recess when my son was chasing him. I remember the teacher telling me about it and said my kid is not punished but he cannot play with the other boy because of his mom's wishes. I really feel bad for that boy.  My son is saying that he is not allowed to play with any of his prior friends and is constantly told to go play with the girls or some of the boys not on the list but he likes active play and the kids not on his no-play list usually don't engage in it.  I know this is not my problem and my son has plenty of friends to play with, but is there something I can do except just making sure the teacher is aware of it -- though I cannot see how she can not see this is going on.  I told my son that I know he feels bad for the boy and I do too but I don't want him to get in trouble and so until the teacher says otherwise he is not allowed to play with this kid since I don't want him to get punished if the boy gets hurt accidentally during play with him or if the teacher sees and decided to say something.  Any advice?  This situation is beyond ridiculous and I cannot believe the school let it get this bad.