The Metzeler Unicross front is DOT approved, and is a full blow dirt knobbie with decent all around peformance.
Food for thought: DOT approval is a matter of submitting a tire to DOT and passing tests. Just because a manufacturer does not submit a tire (for costs and liability reasons?) does not mean it would not pass.
If you want good dirt performance and long life, and are not worried about DOT approval and the police inspecting your bike, the Michelin M12 makes an excellent full knobbie dual sport tire, IMO.