RealUI makes use of angled status bars in its oUF frames.
You can check it out here. It's not a true status bar in that it doesn't actually use that object type, but rather a normal frame with custom methods to achieve the same effect.
It's currently in a transition to a newer design so there are two ways to make them at the moment. The new design starts on
line 164. You can find a use case in the
player frame.
If you have any questions send me a PM.