Going off old letters and journal entries of the time, it seems to have been pretty common, yeah! Even friends who were on tu terms would often use last names to refer to each other. While some people almost always got called by one or the other–or by a nickname– If there was any particular pattern to it at super close levels of familiarity that applied across the board, I haven’t been able to pick it up!
Guys who were less close– casual acquaintances, or school friends but not close school friends, or coworkers, etc– seem to have used last names the vast majority of the time; it would probably be weirder to have men calling a casual acquaintance by his first name, unless the person in question was very young– adults talking to a teenager or child.
(My main sources for all this are of course letters and journals, mostly from Romantics– but since that was Hugo’s primary social scene, that’s close enough to being a realistic Social Norm for him.)
So the Amis using last names for each other a lot isn’t unusual or any particular sign of distance. My own advice to people looking to have them not calling each other by the last name all the time would be to just substitute out with nicknames or terms of affection, which were also very common.
Because otherwise sorting out all those Jeans is gonna get exhausting XD