There is the world that there is, and there is the world that we would like it to be. There is an element of a postcode lottery to it, but I would hope and expect that he would not get any crap from police.
At the moment, he has control over who knows about this. Going to the police would end this, especially if they interview her because it's hard to keep that quiet.
So realistically, when it became more widely known that he has made this complaint, what do you think the reaction of his peer group is going to be? Much that I wish it would be otherwise, I do think it is very likely that it's not going to be sympathetic.
This is one of my reasons for saying that, if possible, contacting her via email / text would be better.