Mods are mods and it doesn't matter if you download them from Steam or Nexus. The only difference is the ease of installation with Steam Workshop. Just go to Nexus and download then install the required mod.

https://www.nexusmods.com/mechwarrior5mercenaries/mods/537 Bobbert has retired from MW5 and never uploaded creations onto workshop. Probably because didn't own a steam version of the title. It is well worth going through the extra effort to get this though as many mods now make use of this handy little mod.

Baradul doesn't list any of the mods that he uses from NEXUS on that steam collection. Probably has a full list elsewhere but listing just the workshop items has confused more than a few new players that want to use his collection so not alone there OP.

It'll work without mod options, but you should definitely get it. It's also perfectly fine when you mix nexus mods with workshop mods, and that mod wouldn't cause an issue with any other mods you may have.

A mod manager may be wise, to help you keep track of what mods you have if you are getting them from 2 difference sources. I use https://www.nexusmods.com/mechwarrior5mercenaries/mods/1085 . Also it allow you to enable and disable mods when not in game, so you can just do that and launch instead of loading, quitting and reloading (when you enable or disable a mod).