Air handlers/ Water heaters in Attic

You're talking code issues? None that I'm aware of in my jurisdiction; don't know about yours. Make sure everything is ducted (no plenums) and make sure you have proper drainage and alarms for condensation and water.

What's the owner's maintenance plan?

An attic location may make it easier for the owner to do routine HVAC filter changes (because maintenance staff doesn't need to deal with accessing individual apartments), but probably makes is clearly the owner's responsibility (because you don't want tenants in the attic). If the air handlers are in the tenant's space then the owner has the option to make filter changes a tenant responsibility.

Water leaks in the attic have the potential to go unnoticed for a long time, and to result in collateral damage to the ceiling below the attic.

Eventually stuff needs to be replaced. Access should make the job easy.