I'd like to share with you what method I foun by accident. With zbrush 4r6 release they change the way slice curve brusch work with dynamesh pollygroups. Its now create extra polygroup inside redynameshed tool, with make old hard surface techniques almost impossible to use ( using autogroup after dynamesh crashes my zbrush quite often)
To make it work the old way (create single polygroup for ich part) turn on colorize option, either on subtool or polypaint subpalette
hope that will help someone, because for me it was annoying and I couldn't find any info about this method