How about have the server.cs files of the add-ons, inside the gamemode, looks like you did that, but have them not in a different folder, just inside the zip/folder, like for the gamemode server.cs,
exec("./Script_PathCam.cs");
exec("./Event_PathCam.cs");
exec("./Event_SetPlayerTransform.cs"); //this is a rename of the server.cs file for the addon.
If that doesn't help, I tried.