Is there a specific cyclocross wheel?
Since no-one has written an answerr for this yet, I will have a go, but be warned I've never done any cyclocross so I'm no expert. So a lot of this is based on gut feel.

The main difference between road and cx are the tyres, in particular their width. Typically on the road you'll ride 23 or 25mm slick tyres, for cyclocross, you're looking more at 35mm or so, with a tread pattern on them.

This can have a knock-on effect with the width of your rim, as a rim will have a range of compatible tyre widths.

So, first thing, decide what tyres you want to run, and choose your rim accordingly. 

You'll need to take account of possible clearance issues between frame/brakes/wheel also - it might well be that the frame you have restricts what tyres you can use, so bear this in mind.

Aside from this, on road wheels you frequently find deep rims, which help with aerodynamics (in particularly for things like time trials). I'm guessing that such rims would be no use whatsoever when you're riding cyclocross, in fact I'd go so far as to say that shallow rims would likely be an advantage. (You can also ride on the road with shallow rims, and in fact they offer better stability in crosswinds, so they are a lowest common denominator,m if you like.)

Does a wheel designed for cx need to be stronger than a wheel designed for the road? I'm not sure about this, but I'd certainly have thought that riding through a field would be more stressful on the wheel than riding on a road. In general, at least. So you might want to look at "sturdier" wheels, for example something with lots of spokes and a strong tangential lacing. I'd certainly be wary of wheels with fancy radial patterns.

You can get bladed spokes on high-end road wheels, the thinking being that the blade faces forward and gives you lower wind resistance. Again, when you come to talk about cx, I can't see how you'd get any gain from this approach, and again I'd be tempted to go for strength over performance.

Lastly, I very much doubt that your choice of hub would make any difference between road and cx.