It's registering a queue to be notified on UAVO changes, not the sensor queues.
edit: that is, in the UAVO system there is functionality to register for notifications on an object change, in which case you can get an asynchronous callback or a message posted onto a queue describing the change. I don't think a queue is strictly necessary for this, but it's a convenient, universally available synchronization mechanism and provides functionality that's useful for describing the nature of the event and registration, which is helpful to the telemetry and logging subsystems. (And is used in a couple other places).
P.S. This is being changed in current code to mostly eliminate sensor-specific tasks and queues, and to collapse Sensors task further into stabilization. It still will be possible to write drivers the "old way", but for things that are processed lock-step with stabilization it's a win to get rid of task stacks and context switching.