converting a wheelset to SS?
 

I'm looking to get a nicer wheel set for racing this season, but most of the wheel sets I'm interested in are for geared bicycles.

Is their any disadvantage to converting a cassette free hub with all the spacers and a sprocket? Would I be better off getting a wheelset built with SS specific hubs?

Because SS specific wheels are not un-evenly dished they are considered stronger than geared wheels. However 90% of bikes (guess) use geared wheels, and they have been built to be strong enough... Just think, DH riders probably beat their wheels up more than any other riding style, and they almost always use a geared wheel. A good geared wheel will be better than a crappy SS wheel.

I thought DH bikes have wider rear dropouts to help with dishing?

Sounds like a great opportunity to learn how to build wheels.

Using a highly dished wheel takes away one of the advantages of riding singlespeed.

If there's one advantage of using a freehub wheel is that you can adjust the chainline pretty easily just by how you have the spacers stacked.