Is there anyway to do this file conversion on a .map or .rmf file from old 3.5 hammer to convert your maps brushwork from DoD 1.3 to DoD:Source?

You can use winbsp or bsptwomap to convert the 1.3 bsp to a map file then open this in hammer then save as vmf.

It carries the brushwork over but obviously you will need to totally retexture and add skybox, change env_model to prop_static etc. Also you might prefer to remove a lot of the floor areas and use displacement instead.

I ported marijuana! to dod source as a test map and it worked ok, even had some nice hdr

So what you are saying is that I can use the hammer in the Source SDK to open up my .Map file and then use that to save it as a .vmf?

That's what I did!
Why couldn't you just try it yourself?

Yeah. That's what I did.

Hammer 3.5 : open .rmf -> save as .map
Hammer 4 : open .map -> save as .vmf

hmm would it not have been easier to just load the .rmf straight into Hammer 4?