Would a Scottish degree be less favoured to an English degree from employers abroad?

No.

No, Scotland's Ancient universities are comparable to England's, perhaps with the exception of Oxford and Cambridge which are considered to be something of a global elite.

The closest thing to a global league table, TES's World University Rankings had Edinburgh as the best Scottish University in 2012/13, and 32nd best in the world. In comparison with other UK universities, Oxford was tied 2nd in the world, Cambridge 7th, Imperial College London 8th and University College London 17th.