I think that flexibility is as important for a male dancer as for a female dancer, but all cases it must be accompanied by an equal strengAth to make use of the flexibility.
First of all, flexibility, balanced with muscular strength, helps to prevent injuries. And even though men are rarely called upon to go to extremes of flexibility in performance, they need to have elegant, easy line.
Men used to be able to get away with less flexibility, but that's no longer the case. My observations are that, at least in major companies, men usually can stretch to at least 180 degrees with each leg, even if they can't hold the leg there unaided.
As to training - many male dancers do Pilates, and often ballet schools will do weight training with them as well. So, from their earliest days, stretching is part of the daily routine, both before, during and after class.