I've read in multiple different places, including here, that bluegill tend to overpopulate even more easily up North than they do in the South (and they're pretty darn good at it down here) because LMB grow much more slowly in the land of short summers. With that in mind, it is very possible that by the time the 3" bass get big enough to exert a controlling influence on the bluegill, if it's the bluegill that got to work right away (can't tell from the photo whether they're bluegill or redear, would have to be a closer shot), that you could have more than they could control.
If your primary goal is bass, you should be fine, as the extra bluegill will give them more food. If big bluegill are your goal, you would be better safe than sorry to add some bigger (8-10" or 10-12") predators as soon as possible. Bass are often stocked a year before the bluegill in Northern climes, upon the recommendation of state DNR's, for this very reason, so they have time to get a head start and can be big enough to control the bluegill when they're stocked.
