Wow I see you got your hands on one. Is he not even addressing their question?
Pictures were going around on WhatsApp.
I'm certain that dayan himself would daven at a chabad house when he's abroad. Would he daven בקביעות at a chabad house? I'm sure not.
He paskens that you are not allowed to daven within 4 amos of a non-frum yid...
On the other hand, he writes that they are allowed to rent space in the shul for their own minyan if they deal with the (non-frum) president, but not if they are renting from the Chabad rabbi...
ETA: The view he takes of Chabad is not that of the vast majority of Satmar. Most of the yungeleit continued to daven in the shul even after this tshuva. The Chabad rabbi was asked to speak to the bochurim of a Satmar mesivta, and did so.