[Kath]

In the film Gimli was pretty clearly a red-head. Irish or Scots wasn't much of a stretch! It doesn't really differentiate the race particularly though because you've also got a Scottish Pippin. The decision to give Gimli such an accent might be related to the fact that John Rhys Davies also played Treebeard and they needed the voices to sound different enough to clearly be two different characters.

There is a very broad range of actors playing the Dwarves in The Hobbit though, so it will be interesting to see what they do accent-wise given they've got a northerner, two Irish chaps, two Scots, a New Zealander ... From the trailer it appears they're just going with however the actor speaks rather than trying to box them all into generic Scottish.