Did Dawnguard add any fast travel to/from Winterhold or does one still need to make the trek up the mountains?

You have always had the option of hiring a carriage.

To Winterhold, yes that's true. However, I still cannot find any kind of non-fast travel transportation from Winterhold to anywhere else.

Walking, Horses riding?

up the mountains ? what route are you talking about there is a nice scenic route from windhelm to winterhold along the coast, if you don't mind the frosttrolls , bears and some nasty master conjurers

Ummm...you've always been able to fast travel to Winterhold.

A truly bizarre post. Like any major settlement you have the option to take a carriage. Once it's been discovered, and like any other map marker, you can FT via the map.

I guess the OP meant carriages? I've always found it a bit strange that the smaller 'cities' have none waiting outside. And if that's the case, no i don't think Dawnguard added any new carriages. It does add a boat in dawnstar though i think that can take you to 'any of the major ports' (Solitude and Windhelm only, and that little dock that takes you to Volkihar castle)