In my current game I was able to evict his Urchin from a Church. But when I tried to infiltrate it with one of my own, I kept getting a message that it was blocked. There are two neutral Thugs blocking it, but the third side was wide open.
And to be clear, if you hire an Urchin here, you get a "blocked!" notification if you try to move him into Sudden Murmur? Can you see which tile flashes red when the notification shows?
Man, I'm stumped! I've recreated basically this exact map layout and situation, and I'm able to get my urchin in the church past my gang. I'll keep an eye on it. If you're able to reliably reproduce it please let me know!