Why would you want to lower the polycount of a zbrushed model?
You guys are missing the best feature.
-Make a low-polygon model
-save Morph Target to reclaim the shapes that will be affected during sculpting
-Smooth it a few times,like 3-6 iterations to make it jump into the millions of polys...yes,millions.
-Sculpt!
-go back to the first unsmoothed mesh,recall the Morph target and export the normal map...Voila!
Same workflow for displacement maps although your renderer will have to support micro-displacement for the results to be identical.
Hope that sheds some lights on the useability for games,if not,well go on pixolator.com and ask away,this isn't really the place where you'll get the most concrete answers about zbrush.
BlackBird thinks he owns the sky,
But he can't look me in the eye,
-Andy Bell