Some weapons in New Vegas in the Energy Weapons class are neither laser or plasma, so they wouldn't benefit from Laser Commander or Plasma Spaz. I'm referring to weapons such as the Gauss Rifle, Holorifle, and the Tesla Cannon, together with all their variants. Would a build using these types of energy weapons be powerful and viable, or not?

They're absolutely viable. The holorifle is basically the best weapon in the game if you're going the energy weapons route, and the other two are at the top of the heavy hitters as well. They can definitely carry you through the endgame.

they're alright but you cant constantly rely on them due to lack of ammo and durability