Currently equery list does not honor the ROOT setting so you can't list installed packages from another root properly. The current broken behavior is that only packages that have the same version in "/" and in the ROOT are displayed. I will attach a very simple patch which fixes this.
Created attachment 89198 [details, diff] Patch to get equery to honor ROOT
Thanks for the patch. Patch is in svn rev 300.
This is in stable portage for a while so I'm closing it.