While they won't fight to the death or anything like that, you SHOULD keep an eye on them. Sometimes, this sort of behavior can be very stressful, particularly if one male is getting the brunt of it, which can lead to problems. If it DOES become a problem and the one starts to show signs of being overly stressed, you have a couple of options. One would be to remove the aggressor or the lesser male. Another, if you have the room to do so, might be to add some females to the mix (suggested ratio is two females for every one male).