It may not look nice sitting on mulch, but it won't stain it either. Spread it first, then mulch. Or cultivate it into the mulch that's there.
Treflan is an ingredient in Team & TeamPro. But at much lighter rates. The 5% trifluralin prills in Treflan 5G will smoke bluegerass if you let enough stray. Watch for steep hills if just broadcasting over mulch since it can harm the turf, especially on the down slope side.