At this point God is a long way from omniscience. He admits that he's acting on hearsay, and allows himself to be shamed into sending in the angels to see if they can't find ten righteous people in the city, in which case he'll reluctantly agree to leave it alone. Of course these angels stop at the first house they come to, which just happens to be Lot's, and never get round to carrying out their divinely appointed survey. Maybe that's just as well, since their definition of 'righteous' seems to include a guy who's willing to let a frenzied mob loose on his own daughters, and even goes out of his way to advertise the fact that they're virgins.

But then they were working for a deity who only a few short chapters earlier had thrown his toys out of the pram by exterminating almost every living thing on the planet.