Some of them, yes.
You can use the BritRail England Pass on the Cornish Night Riviera sleeper train.
You can use a BritRail Pass for travel on the Cornish Night Riviera sleeper and the Caledonian Express.
Note that, on both of these, a berth MUST be booked prior to travel and there is a fee to do this. However, it will be much less than if you booked the train as an individual journey.
