He fought fairly closely with an extremely talented weapons master before he became Naga Sadow's apprentice, yeah.
Indeed, though sources disagree on whether it was Naga's spirit, or if he had preserved himself via stasis. The latter makes more sense considering his spirit supposedly faced Jedi Master Ovair later on.
He probably found himself in multiple skirmishes with Jedi during his travels.
Regardless, I think this makes him pretty interesting as a warrior. I mean, an alchemically enhanced blaster pistol as his main weapon? That's pretty unique, and apparently very effective.
I imagine it's much like a TOR flashpoint, yeah.
In fact, the battle itself was probably very similar in nature to Bane's own battle against the Jedi Strike team on Tython. On that thought, it's very likely that he himself donned a suit of Orbalisks during his reign on Onderon, which is an inherent combat advantage.
Indeed, he even has quotes calling him the greatest Sith Sorcerer that had ever lived, (presumably up to his time) and that he had mastered virtually every Force Power, including many that were thought to be lost or hidden. Even if it's not a feat, I find it pretty cool that both Exar Kun and Darth Zannah and others learned most of what they knew about Sorcery from his knowledge base.
Let's not forget that even as a spirit, a shell of his former self, he has some pretty viable feats. When Vodo Siosk Baas-one of the most powerful Jedi Masters-attempted to contact his apprentice through their Force Bond, Nadd reached out from across the galaxy, rebutted his attempts, and forced him to his knees. He also healed Exar Kun after the latter had broken countless bones in a rather impressive showing of mastery.
I'm maybe speaking a bit over-enthusiastically, but I really don't think you're giving Freedon Nadd enough credit.