In Viz Goku says "He looks slow" about Yakon, and Yakon's speed caught him off guard. Seemed his assumption got him in trouble there. I suppose an argument you can make is that Kaioshin seemed to make it clear that Dabra was the top guy, so everyone else by virtue would be weaker than him.
Also looking at Vegeta vs Pocus, he actually gives no insight as to his power. All Goku says is that he disagrees that Pocus will win, but that goes along with the point that Dabra is already established to be the top guy. Vegeta even takes a defensive stance against Pocus at the beginning of the fight, so I'd say they have no clue how strong he is.
I wonder if Kaioshin can sense him though due to being a god.