Parker Parvex motors are available which are explosion rated to Class 1 Div 1 Group C & D (Liquids and Gas).
Parker does not have a vacuum or explosion rated STEP motors.
Empire Magnetics may be able to help you with these types of applications or for servo motors with Class II Div. I Group E, F & G. Here is their company information:
5780-B LaBath Avenue
Rohnert Park, CA 94928