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If by "Poly Wave BWF" you mean multi-channel WAV (with or without SOME BWF chunks), Reaper can work with them internally since it supports up to 64 channels per track.
 
If you mean specific device encoded chunks... I guess DAWs are unable to preserve/write them. Reaper framework allows read such information, and with some tricks even write. So, theoretically possible, but google have not found any examples.
 

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DAWs prefer to work with separate files since that is more efficient during processing. F.e. when you bounce/glue some clip/item, there is no need to copy the whole multi-channel WAV, just what is really copied/pasted.
 
Reaper can render into up to 64 tracks single file. So it can "export in assemble" without any extra step. My concerns was about particular device into which such file is loaded. Special "apps"  can put something special in the header, and that can be different from what Reaper writes there. I guess the only way to check is to try...
 
Note that Reaper support "extension", also for exported files. That means anyone (with sufficient skills) and motivation can write support for any (audio) output format (in case it is known).

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