I don't think they should. First of all, there is the possibility that the male (I really hope he is gelded) will retain some stallion characteristics and could really bother the mare. Also, you need to be able to control who eats what (grain, supplements, hay, etc) and this would be very difficult if they shared a stall. Plus, if one of them got sick it would spread immediately.
They should be fine, given that the get along and theres plenty of space, and the male has been castrated, unless you breeding them of course. i would keep an eye on them though, just incase they suddenly do take a disliking to the other, also illnesses like strangles is very contagious, but they should be fine.