NATS is looking first and foremost for candidates suitable to become ATCO's.
In the early stages of selection they want to see that you have the correct tools in your box so to speak. I cannot imagine that they would differentiate between disciplines at an early stage and so I guess the answer to your question is no. If you look at the thread about the March course then you will see that people are chopped and changed at the last minute, this would be impossible and far less flexible if you were recruited on the basis of one area of ATC.