This document describes what qgis_wms supports/ does not support

LineSymbolizer:
Geometry					No, use feature geometry
Stroke: GraphicFill				   No (let's say not yet)
Stroke: GraphicStroke				   No
Stroke (CssParameter): stroke			   Yes (RGB)
Stroke (CssParameter): width			   Yes
Stroke (CssParameter): opacity			   Yes (note: UMN mapserver does not support this)
Stroke (CssParameter): linejoin and linecap	   Yes (note: UMN mapserver does not support this)
Stroke (CssParameter): stroke-miterlimit	   Yes (note: UMN mapserver does not support this)
Stroke (CssParameter): dasharray		   Yes
Stroke (CssParameter): dashoffset		   No

PolygonSymbolizer:
GraphicFill					not yet
Fill (CssParameter): fill			yes
Fill (CssParameter): fill-opacity		yes

Point Symbolizer:
Mark symbol		only square, circle, cross and x (star is not supported)
External symbol		not yet
Size			yes
Opacity			yes
Rotation		no