First of all : The Waffen-SS was never the elite unit that some people have you believe, and they were certainly never the best trained or equipped soliders. Actually in the earlier stages, when Waffen-SS units were deployed for the first times they often suffered heavy losses due to inability of their officers. /u/Zinegata wrote a good writeup here

For your actual question : It's as simple as : There were no Waffen-SS units organically attached to the 6th Army at that time, so no units could fight there. The Waffen-SS units were usually deployed in a frame of superior Wehrmacht units/commands. They were not dispatched individually on a regular basis.