Perusing the Sky and BT community forums, and also Reddit going back two years, and the lack of Dolby Atmos on the Ultimate channel seems to be recurring point of complaint, particularily since the switch to TNT Sports.
It also seems to be an issue, although to a lesser extent for those using the Discovery+ app. When it was BT Sports it was the norm, especially for European Football, however now it's very unreliable and seems to be even more selective in the events that they do decide to broadcast in Dolby Atmos. Yet they usually manage to broadcast DA on channel 521, as they did with todays match.