I too would say that you need to have the disconnects interlocked with the door but whether or not you can do what you are suggesting will depend on where you are and their local laws and regulations. I feel that here is a lot of opinion floating around here that is not necessarily factual.
NEC states that you must have a disconnect. The door of that disconnect must be mechanically interlocked. This disconnect does not necessarily have to be in the panel. The disconnect can be seperate from the panel according to the NEC.
The NEC does not govern equipment though, except for 1 article that is rather short and unsubstantial. NFPA 79 is the electrical standard for industrial equipment and, at least in my state, is technically optional. In other countries manufacturers must produce safe equipment to a set of standards. In the USA the burden is on the employer. Equipment manufacturers can sell equipment with no guarding or lockout points if they wanted to, but the employer using the equipment would have to implement those devices.
OSHA lockout/tagout regulations are there to require lockout points and layout requirements for safely locking out equipment. They are there to govern the employers though.
NFPA 70E is safety requirements for working on electrical equipment. There is a section talking about disconnects having interlocked doors, but again this does not necessarily apply to the panel of the equipment if the disconnect is seperate.
I'm currently gently prodding my employer as they use a lot of multiple disconnects. I've done a lot of gathering of evidence and technically, at least in Texas, you can use multiple disconnects for multiple power sources on the same equipment as long as the disconnect can be locked in the off posistion, cannot be locked on, has an interlocked door, and meets labeling requirements.
This is not the way that I feel this should be done though. The best suggestion I have seen it to use a cable operated handle that can operate multiple disconnects or breakers. I would interlock with the main enclosure door. This is assuming this is a relatively small application. For a large modular multi-door (4+ doors) application I would provide a lockout point from a separate breaker panel, load center, or switch gear.
Long story short, yes you technically can even if its not a good idea. It is far from recommended, it is not in a published standard, and if someone is injured there may be lawyers involved asking "To what standard was your equipment designed to and considered safe?"
