Whilst none of us here are privy to the details of the license, I suspect that the issue that Hornby had with Bachmann before was the selling of a model developed FROM a Thomas loco (Thomas and Percy sans faces in the digital set), which I can actually understand. If you have spent a lot of money marketing and developing your engines, then you don't want another company making profits from their competing range if they have not won the license themselves.
However, I suspect that in due course we shall see Talyllyn and Dolgoch appear in the Bachmann 'proper range', as they are models of real engines, not fictional ones. Provided that they never officially sell Skarloey or Rheneas over here, I can't see any way that Hornby could challenge them legally.