Well, they started out as Crusaders, so I'd guess they'd be less welcoming than the Wolves in the early 50s, though one imagines better than the Falcons or Jags (their Care Bear nature can't have come out of nowhere). Their big change of heart didn't come until many years later (which, remember, is several generations of Clan warriors). My sense is that in the invasions, units like the Maulers with their death to mercenaries attitude were more the norm than the exception (one wonders if this wouldn't have helped rather than hurt with the FRR people later on). And in any event, even a large portion of the Wolves weren't totally on board with Phelan, so if we believe the Bears had more of a Crusader attitude then it would stand to reason that until the late 50s when the Bears began contemplating relocation the prospects for an IS bondsman would be... frosty?
Though even the more hard line Falcons have at least one IS bondsman who became a Star Captain, so it's plausible that a Bear bondsman in this period could become a warrior at least, if they were exceptional.