In their natural state (ie feral and out on the range), bachelor groups of stallions will form and hang out for safety. These are usually young inexperienced stallions who are ousted out of the herd by the seasoned stallion (or top stallion) of the herd. So depending upon personalities, lots of pasture room and the absence of competitive interests (eg mares), they may get along. The thing with stallions, though, is that I think they are always loaded for bear -- if a dispute does erupt they'll haul out the automatic weapons and the end result is never pretty.