Multiplayer game question...

That's a good and important question. 

The DM maps use to require a DLC if you used a DLC item, but not otherwise, but that may have changed (for the better, but not sure).  For my own DM on Steam, I have a version without any DLC marked items, and another version with...

There is a better chance of an answer on the Solasta Discord channel (the link is the official Discord invite, as seen at the bottom of this web site).