[The Saucepan Man]

The quote I gave above seems to imply that it was indeed Uruks riding the wolves, since Merry at any rate does not distinguish between them and other orcs.

The quote is inconclusive, particularly as Merry is likely to have limited knowledge of different Orcish strains. Also, from a distance, the different types are likely to have been indistinguishable save in size alone, and it would therefore have been natural simply to use the generic term to refer to all of them.

But, then again, the quotes that I gave from UT are inconclusive too.

My belief that the wolf-riders were not Uruk-Hai derives primarily from two points.

First, I agree with Mister U when he says:

Although large, the wolves were, I think, nowhere close to horse-sized as portrayed in the movie.

It seems to me that Uruks, being man-sized (or perhaps bigger) would have been too large to ride Wargs comfortably.

Secondly, the Warg-riders that we meet in the Hobbit are Orcs of the Misty Mountains. We know that these cave-dwellers were small in stature, and we know that they did indeed ride Wargs. So, makes perfect sense to me that the Warg-riders employed by Saruman were Orcs from Moria, or possibly other cave settlements in the Misty Mountains - perhaps closer to Isengard, that he had pressed into his service, rather than being the Snaga of Mordor.

On a side note, I envisage Snaga as being smaller even than the Misty Mountain Orcs, so that two Hobbits suitably attired could quite easily be mistaken for them.