The rental limit on a condo building usually means how many apartments are rented out of the total number of apartments in the building. It doesn't pertain to the number of people in any one apt. Now sometimes there are limits from the association on how many people can live in an apartment but it sounds like you are talking about the number of units rented. So go ahead and get a roommate. Make sure you set ground rules for the tenant to follow.
Do you live there and are looking for a room-mate? If so, then you shouldn't have a problem.
However, if you're looking to rent out the entire unit to a new tenant then, yes you may have an issue. The rental limits are in place for a reason.
Normally, the reason for rental limits are due to FHA qualification guidelines.
Hope this helps!