AoW PF cut down massively on the number of barracks. There is only 3:
Skirmisher (anything shooty that is not a core unit)
Specialsits (healers, supports, casters)
Elite (most T3 and all T4), wich you unlock with the first unit that needs them.
And you can totally cram them all into the same city.
However there are a handfull of units that can not be build conventionally. Promethean Plasmoids, anything from Xenoplague, Kir'Ko emergent. Only opeartions or effects of units can spawn them.
Finally there are a few units that are only combat summons. You get them via a Tactical Opeartion. And they despawn after combat. Wich also means modding them is not possible.
But the Excavator Tank is simply a Elite Unit, so the Elite baracks will be nessesary. It is worth pointing out that the Dvar Baron is a T3, but not an Elite. Simple Specialist Baracks work. That is rather rare and also means you did not had not built them for the Baron.
Of course for the Hero vehicole version, you equip it as a primary weapon. Note that you do not need the proper Baracks anywhere to equip a Vehicle onto a Hero.