If you want to put the mod running in the server you have:

1- copy the mod from Steam mod Folder to the Game Mod Folder.

This is the mod folder in Steam C:\Program Files (x86)\Steam\steamapps\workshop\content\228380

copy the folder name: 764432700 to the Game mod Folder located here: C:\Program Files (x86)\Steam\steamapps\common\Wreckfest\mods

2- you have to put the mod in the server_config.cfg
look for the line in the file and write mods="mods names you want"

Example:
# Server update frequency: low, high
frequency=high

# Mod folder names in a comma separated list
mods=764432700

Then you can run the start_server.bat. If the mod not loaded or when you try to enter the server you can't. Stop and Restart the server one or two times and the mod load up, the same if you get out the mod from the config file, for the event take place you have to stop and restart the server two times.

Remember copy again the Mod from Steam mod folder to Game mod Folder when the mod from Steam Update.

Sorry for my bad english, i am from Argentina and Spanish is my home language.