Run into this recently.

Hid a table from camera in Poser so that I could place the camera without it being obstructed by the table but still wanted the table rendered in an opposite mirror.

Worked great.

Not sure if the same technique could be used via Reality because of the unbiased nature of Lux...?

The various 'hide' options in Poser at first might seem confusing but are there for their own respective purposes.