Well, unfortunately I couldn't find mention of Rev B in the help. Besides generated xml file doesn't contain revision definition in its header so I'm not sure what version of IPC-2581 is used by Pulsonix export.
At present we have only one PCB fabricator who indicates that they accept IPC-2581. The main purpose I have for this output is to import it into the free version of Mentor Graphics Hyperlynx for some extra DfM checks on a small number of boards.
I note this morning that Ucamco are proposing adding two new Gerber layers to describe component assembly data for the top and bottom sides of a board in the next version of Gerber: Gerber X3.