The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
As of now it is impossible to play Nomads in the regular campaign. Nobody is working on changing this. Also I don't know if this is possible (Nomads would need to be turned into a regular mod - but as far as I can see Nomads is no longer developed - so also I do not believe a Nomads campaign will come).
Setting up offline fa exe and then loading up the skirmish missions. Is easiest way. Then cheatspawning nomad acu. SCTA Mods also provide a means for this w/o cheatspawning!