Arma 3 can run in three different ways:
SP: The program runs with no connections.
Coop: The program runs with connections over lan and inet, but this is not a dedicated server (Supports MP gaming)
MP: A fully dedicated server that only accepts connections to play MP games.
The Arma 3 executable is different from (SP/COOP) to Arma 3 server and internally dont work in the same way.
One mod can run in (SP/COOP) but no in a Arma 3 Server.
Usually the mods has code to work in every way possible but in a well designed code you need create a version for Arma 3 client and another for Arma 3 server.
Thats why I have two separate versions one for Arma 3 client (sp/coop) and another for Arma 3 server.
Programming that way you can achive maximum performance and avoid redundant code (thats why exist an Arma 3 server executable instead using the same executable for all).
But sadly the devs are creating a big confusion mixing in his poorly documented (without any code examples) the same concept for MP games.
A MP game can be created using the client or server but internally dont work in the same way.
The SP/COOP version dont work on server side and the MP (Server side designed) runs in server.
In the professional world a client cannot be used to run server task and theres client designed software and a server side program to fullfill this task.
Is very confused but isn't my fault, is a decision of the devs and his network architecture.