Hi, thanks for your question.
First of all TruckersMP supports all Steam DLC that is sold, Simulation 1, Simulation 2, Arcade and Event servers will be able to get the DLC for the maps you have, but Promods servers have to be satisfied with the map DLC and you will need to go to the official Promods website to download the Expanded Maps Pack which is based on all the map DLC! This is an extension of all the map DLCs. The DLC you bought on Steam is supported, if you have other maps please go to the official mod (we call it Offline Mod Online), you can subscribe to it and activate it in the Creative Workshop, but it does not support TruckersMP.
Best regards.
Yu Jian TMP