Can apartment complexes get into legal trouble if they withhold important information concerning their residents?

Unfortunately, there is probably nothing you can do about the failure to provide information about the drug ring--there is no general obligation on businesses of any sort, or indeed, on any persons, to discuss or provide information about local crime committed by third parties. And since there is no obigation to provide this information, an apartment complex may require or instruct its staff to not discuss it--and punish them if they do not follow that instruction.

The only exception where there could be some legal consequence for not providing information relating to local crime would be if on signing on renewing a lease, a tenant specifically asks about crime; in that case, if knowing of local criminals or criminal activity, the apartment complex lies about it, that could be fraud, and could give rise to the right of that tenant to break the lease (void it) or seek monetary compensation.

However, a landlord is obligated to provide "reasonable" security for tenants, and what is reasonable is judged in part by neigborhood conditions. If your neighborhood is known to have a lot of criminal activity, your landlord may have to do more to counter it--e.g. more lights, security patrols, etc. If you have suffered damage or losses because your landlord is not providing adequate site security in light of local conditions, it is possible that you may have a lawsuit or cause of action against the landlord. It would be worthwhile for you to consult in detail about the circumstances and your losses with a landlord-tenant attorney, to see if you might have a viable claim.