My working hunter pony, Chance, has a splint on her near fore which she threw about two years ago. No judge has ever commented on this and they have always said she has very good conformation. I compete Chance all over Cheshire, Warrington and North Wales, we have qualified a number of times for Uk premier, BHS North West championships, Festival of Champions and Ponies UK, we have gone to the qualifiers and again at that level no one has commented.
Conformation isn't important that much in Working Hunter incomparison to say, an inhand class but it is still important and often is not the deciding factor. It would only come down to conformation if you were on the same points as another after the jumping and individual show and the turnout of both pony and rider was the same also, then it would go down to the comformation of the ponies. However, it is rare that you are on the exact same points as another by the end, but if you are then it is almost always down to your turnout and 'whoever is more workman like.' Also in with the turnout is things like if you have banded your plaits in or sewn them in, sewn is generally better than bands but then again not all judges check your plaits.
Hope this helps! SM xxx