Unluckily, I can't imagine there is any disassemblers that will output C or CPLUS that is aware of the PM functions. Strictly speaking, a disassembler outputs assembly language, hopefully with generic labels and such. While possible to output C, it would probably take quite a bit of manual intervention by a knowledgeable programmer to get something that looks useful rather then just capable of being re-compiled. IDA does seem to have its own C type language that it uses.
The NSA tool could be pretty powerful and who knows, it might even support disassembling OS/2 as the NSA is interested in looking at everything.
Usually, I believe, disassemblers are mostly used for things like removing shareware limits and other types of copyright protection as well as fixing bugs. The more complex stuff you want to do, the more knowledgeable you need to be.