My view is that the city of NYC knows about the vampire lord living there. The neighborhood of Sesame Street is his territory, the dealers and gangs know this, so they avoid it. The government would have sent people in to deal with him, but he is useful.
Personally I figure it's not *just* the Count- one vampire can be avoided after all, especially during the day.
But also? Oscar's there. He's just hanging out in the trash can all day and he sees what's going on. He can make some comments- if anyone comes after him he can retreat into the can. And he can pass on what he knows to the Count. Heck, the humans do too.
It's a community effort, and the Count's just part of it.