Avatars are loaded from the save entities and faces directories that the Client and Editor usually use. Since the server is the one sending them, in this rare case the server actually needs the resources.
For completeness and coverage of potential future features or enhancements, please copy the entire Editor resources directory (don't copy resource packs meant for the client!) to the assets/editor directory (you may need to create this!) in the server's working directory.
At a minimum, the entities and faces directories are required. In the future, the paperdolls folder will also be required.
As shown in the below screenshot, assets should be a sibling directory to the normal logs and resources directories of the server, and the editor resources are located in assets/editor/resources.
