I don't doubt that sexual assault on men is most likely under-reported due to a combination of societal pressure and sexist culture, but I think that the cases of sexual assault on men are definitely fewer than those of sexual assault on women.
I can cite my own experience: most women where I live, including close family, have experienced sexual harassment at one point or another during their lives. Furthermore, a lot of them were told to dress or act differently to prevent sexual harassment. On the other hand, none of the men I know have ever told me that they have experienced sexual harassment. Most of them have no reason to fear telling me, so I take it that they haven't had that experience, just like I haven't, thankfully.
It seems to me that it takes an exceptional amount of oversight to claim that women and men experience sexual assault and harassment equally often.