Apologies for the late reply, its crazy busy at work right now!
Thanks very much, displacement maps were used to help bring out some of the extra detail. We used the texture detail itself however this obviously isn't an accurate way of doing things so you need to be careful what you displace.
Make sure you have a morph target saved and are working on a layer. You will need to morph target area's back to their original state. There is also a fair amount of hand sculpting involved with general cleanup of the model. My favorite brushes for this are the flatten, clay and dam standard. I try not to use smooth if possible as I feel it can sometimes destroy too much of the underlying detail.
The majority of tricky fine details were created by hand, I myself like using the standard brush and the dam standard in different sizes and intensity however my colleague prefers the slash brush.
So the answer is no we aren't using any special brush's/alpha's. I'm unlikely going to be able to show you our entire workflow due to competitors unfortunately however I'm more then happy to try and give helpful tips where I can.
I would say layers and morph targets are key with this level of detail though.
Here are some of the Nike poses rendered in ZBrush