So, I've been playing some Nasus on 3v3 recently. Normal build, GP/5 tanky and Tri-force. Whenever i solo queue people complain that "Nasus can't get enough farm on his Q to be effective" in 3v3, but I find that I tend to carry the team around 30 mins, as Nasus can defend quite well.

He's OP on 5's, yeah, but any thoughts on whether he is viable on 3v3?

Nasus can be strong it does just depend on your and the enemy team comp.
In Blind you don't know who you will face thus nasus is more like a gamble.

Nasus is strong late game if you build him with health for survivability. I've played some non-ranked games with my team and when we ran into a Nasus it was bad news bears. He was surviving like crazy and he was doing quite a bit with his Q