I've only ever seen dogs yawn on purpose as submissive/appeasing behavior. Kind of a nervous "I'm not trying to cause trouble." I'll get it from dogs if I've asked them to do too many behaviors in a row and they think it's because they haven't given me the correct one. Kind of an apology that they don't know what I want.

I see it occasionally between dogs when one is being stiff/dominant and the other yawns to kind of apologize and diffuse the situation.

Then again, I haven't worked much with sighthounds and they're basically a different species from other dogs, haha.