Hmm, I'd agree that there are similarities but on a whole I think the UU is simpler than the HxH Power system which is far more complex.
Nen from HxH has 4 Principles: Ten, Zetsu, Ren, and Hatsu. The Un-power in UU can be parted in two - negating rules for yourself, negating rules for others.
Nen has advanced techniques, 6 types of individuality, Aura types and so on. UU focus so far purely on the negating aspect which is funny in a way as most negation (expect Andy's) seem to need to meet some condition to be activated. You could take in the UMAs as extreme versions of the rules themselves but they are more like "out of the battlesystem" since they are the bosses the negators have to fight to fulfill the quests given to them.
But in a couple hundred chapters, if UU runs for so long, the Negation System of UU might also advance in complexity like Artifacts which we saw a couple of for example or using UMAs as tools in battle. Or ofc Weapons made by Unbreakable.