Surely one wouldn't fly any fast jet without a working seat?
Yes they do in the civil world, its all down to the cost of certification, spares and training available, mainly due to the CAA costs, so the easy option is to de-activate the seats, you still have the option of jettisioning the canopy and bailing but of course not as easy said as done in a FJ.
Not saying this is the case with the jets in question just responding to SSD's post.