While a 12 gauge shotgun can be the equivalent of a powerful rifle, I believe that the use of buckshot is a very specialized one and one that is mostly misunderstood. By the time that the shot pattern has opened up enough that you no longer have to carefully aim, buckshot has ceased to be the proper tool. Each pellet is very light compared to the combined shot column weight, therefore each pellet looses velocity quickly and without velocity the pellet cannot penetrate deeply enough to cause a lethal wound. Secondly, shot depends on a number of hits in the same place to increase the seriousness of the wound, the wider the shot pattern on the target, the less lethal it becomes. Buckshot doesn't have many pellets to put on the target so it's effective range is determined not only by the velocity of each individual pellet, but by the width of the pattern. The tighter the pattern, the less survivable the wound. That means that when used within it's effective range, the shotgun loaded with buckshot must be aimed just like a rifle Out to 10 yards is about the limit for buckshot on a big animal, beyond that a slug is the better tool.
The reason to choose shot over a slug is then not to make hitting easier, it is to limit over-penetration that could be dangerous to other people or cause property damage beyond the target. That being the case, having the first round out of the magazine loaded with buckshot could be viewed as sensible. The shotgun so loaded could then be effective at close range, but should the first shot needed to be taken at longer range, the shot cartridge could be simply ejected and a slug loaded and fired. In almost any possible scenario, a follow up shot should certainly be made with a slug if the animal is running for cover.
The reason we prefer rifles here for bear work is that in a situation where the bear monitor is responsible for a crew working in a wide area, or a group of tourists strung out along a trail, the need for lethal force might be beyond the range of the shotgun, even when it is loaded with slugs. Depending on the layout of the camp in question that might also be a consideration.
With regards to the magazine capacity of a .303 or a .30/30, while that capacity might be comforting, if the problem is not solved within 3 rounds, it probably won't be solved then and there. The bigger question, than if the camp gun will be a rifle or a shotgun, should be who is going to be the designated hitter. Preferably it is someone who has some hunting experience and has killed a large animal in the past. If the bear problem is significant, hiring an experienced bear monitor is better than arming a neophyte and giving him or her the responsibility of protecting people.
The suggestion to booby trap a bait with poison or a chemical that is more likely to injure than kill the bear is of no value what so ever. Aside from the cruelty issue, it could result in a very dangerous animal near a populated area should the bear survive, but be unable to feed itself. I have no problem with killing a bear in either a hunting or protection scenario, but to me this line of thinking is despicable. If a food conditioned problem bear is in the area, get the DNR to bring out a culvert trap. If you shoot the bear prior to it being caught, then that solves the problem.