I have never noticed overt collusion. The players keep the game pretty clean. It's no different than Gemini for example. If anything I see less angle-shooting at NST. I've seen people kicked out for being drunk; Joe runs a pretty tight ship.
Of course I'm sure shady things happen in all card rooms, but I've never seen anything that stood out. There are a lot of regulars, and they all seem to be there to either make money, or feed their gambling addiction, or entertain themselves. I don't think any of the regulars would stand for collusion.
Sometimes when a particularly bad player leaves after spweing off their stack, people may comment on their play. They may say things like "yeah he always comes in Friday drunk and donks off his stack". I don't think that's collusion, just general table talk. Hell, they may have said this about me at some point