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On the official wiki, it says copy over some files from directories which don't exist in the gog version, and says "(especially DUKE3D.GRP and DUKE.RTS) ".

Especially implies those two files are important but not EVERYTHING. I'm confused. I copied them over and the game SEEMS to be working, but for all I know I'll get halfway through it and then sounds or textures will be missing.

Are those two files ALL I need from my GoG install? The wiki's wording doesn't make it seem so.
All I put into my eDuke32 folder is the DUKE3D.GRP (and then the optional High Res Pack files associated with it) and it's been working fine for me. Maybe I should put in DUKE.RTS too?

Additionally, I've also used the GRP files for Duke It Out In DC, Duke Vacation and Duke Nuclear Winter (the unofficial expansions).