I certainly agree that positional balance within a class is important, but I'm not too worried about this yet.
In addition to cross-training them as corners, as you mentioned, it's certainly possible that some of the HS safeties will grow into LBs.
Beyond that, the college game seems to be moving in a direction of more 3+ WR sets, so having extra nickel DBs is always handy. Not to mention that special teams are often heavy on players with safety-type skillsets. Finally, anyone who saw USC play last year can see that this program is in serious need of an infusion of athleticism. I think it makes some degree of sense for Beamer to focus on bringing in the best possible athletes regardless of position, so as to raise the overall athleticism across the roster.