It would seem to me that, in theory at least, you could inadvertently go over the cap if you have a half dozen or more players arbitration eligible, and all or a majority win their cases at far higher salaries than could have been imagined. To me that's different than someone going over the cap in this initial draft, which would have to be considered intentional.
You do need to have some cap space for arbitration no doubt, but if you've been carrying 3 players at say $1 the year before they become eligible for arbitration, and all have exceedingly good years, that could cost you $12-15 million additionally in salary if they come in even as low as $5-6 M. It's hard to see any team having that kind of cap space under those circumstances.
Yes, it's the arbitration rule that could put you over. We need to plan for arbitration carefully. Since arbitration is settled after the free agent signing period, there is a significant risk of going over if you have not reserved enough salary cap to cover your worst case scenarios.
I like the suggestion of benching arbitration winners first to get under the cap, but I'm willing to consider any penalty, although I think we need a serious one in order to force GMs to properly plan and manage their caps in advance of arbitration.
The second potential area for mistakes is the league minimum salary rules. If you fail to account for salary increases for plavers under control you might slip up there are well, although the salary amounts are small. You also can't forget to withhold $1.5 mil for new prospect signings each year (until you reach the 10 player max).
Phil