Personally, none of mine are aggressive, but some have seen aggression. Usually, however, as long as there is no female to be competitive over there, enough food and enough space, they should be fine. Just be prepared to separate if you have to.
Northern red-footeds are not usually aggressive, but Southern (or 'cherry-head') often are. The key is space and resources- there needs to be plenty of space, several hides, several feeding stations, etc. Most keepers find their red-footeds get along just fine- even sharing hides and feeding stations- as long as they are not stressed (crowded, etc.)