In Class II locations, proper electrical area classification is largely a matter of housekeeping. I usually encourage clients to (honestly) review their housekeeping practices closely.
Assuming the location is correctly classified Class II, Division 2, equipment selection is usually straightforward.
You will find it difficult to find a NEMA 12 motor. NEMA MG-1 just doesn’t classify motor enclosures that way. Newer motors are more likely to be identified with a “degrees of protection” (IP) mark. You will probably want IP6x, although particle size may permit IP5x. Even more likely the enclosure will simply be described as “Totally Enclosed” such as TEFC or TENV, or possibly dust-ignitionproof. With exceptional housekeeping some open-type motors are acceptable. I usually don’t recommend open-type though and generally prefer TEFC. I highly recommend IEEE 841 motors.
NEMA 12 would be acceptable for switches; however, other environmental conditions beyond dust should also be considered and NEMA 12 alone may not be sufficient. Dust-ignitionproof is not required.
You don’t need explosionproof seals; but, depending on the raceway orientation, you still may need some form of dust ingress prevention. Reread 502.15 and review your raceway installation. If you still need to seal the FPN notes electrical sealing putty is acceptable.
Robert B. Alexander, P.E.
"I know that you believe you understand what you think the NEC says, but I am not sure you realize that what you read is not what it means." (Corollary to Charlie's Rule)