Regarding using the 208 high-leg for 208 volt loads...
I think it is generally accepted that single phase 208 volt equipment is designed for 2 hot legs of a wye system. Although "generally accepted" dosen't constitute a code rule, using a single pole "slash-rated" circuit breaker would be a violation of 240.85. Although I have used "straight rated" 2-pole CBs on delta systems, I'm not sure they are available as a single pole device.