Three things:
1. Gozu is capable enough to get anyone off of him
2. Gozu, being privy to his NG, would not allow someone to fall asleep on him in the first place.
3. Because they are put to sleep at regular intervals, it stands to reason that falling asleep outside of the sleep timer stuff is unlikely.
As such, Gozu is only realistically at risk of having his NG used against him by Monaka or the attacker. Monaka, being a lurker, likely didn't do anything big aside from killing Gekkogahara. The attacker, being the attacker, means that the pool of potential perpetrators is highly diminished - having only one person who would use his NG against him instead of 15. Anyone can punch Asahina and anyone can commit violence in front of Bandai.
As I said before, it's all too interesting that Bandai's was the riskiest and Gozu's was the safest, and they are the people we know the least about.
On the subject of NGs, many of the NGs have very significant themes. Izayoi can't eat Ruruka's candy (that he loves), Ruruka can't let anyone leave (literally and figuratively), Chisa can't let Munakata die (because she loves him), Makoto cannot run in the hallway (because being a kind of regular person, he gets a regular limitation), Gozu can't be pinned for three seconds (because he'd "lose"), Kyoko cannot survive with Makoto (basically to contrast her arc, where she originally was willing to sacrifice him in 1 in order to discover the truth). The ones I cannot attach direct themes to are Kizakura's left hand, Aoi being punched or kicked, Seiko's shadow, and Tengan's lies (though I have an idea). I think that Kizakura's was meant to lead up to him having to save Kyoko by risking his life, but if this is the case, it was a little clumsy because it requires a lot of coincidences to create that situation.
But Tengan, let's assume that Tengan has a theme to his NG of answering a question with a lie - and as such, it stands to reason that Tengan is a liar. I am predicting that before the series is over, we will see that Tengan is responsible for something horrible, and that he was the one who pushed for the Kamakura Project.