dwm, as wmii also, does not depend on xsetroot. It's like a running gag with that xsetroot dependency... Reproducible: Always
Could you possible improve that attitude there? It's getting annoying.
The ebuild really depends at runtime on xsetroot as it is used in the session script to update the status bar.
Shouldn't that be changed then? I think the minimal (as in minimal USE flags) version of an ebuild should ship the minimum of the package, not optional components that are not part of upstream releases nor recommendations such as a session script. Maybe make it an "X"-useflag?