Thanks for the advice ! I will file it with "Don't smoke in bed".
Perhaps you did not see the word "theoretical" used in the post. I am just exploring a possible HACK to run 2 cameras on one cable run.
If you know for a fact that the Dahua only supports one protocol or the other and that trying the wrong protocol will cause damage then that would be extremely useful.
How do you think that POE came into existence. Somebody pose the question "hey we got 4 conductors in that wire that isn't being used ".
I know I have used the extra pairs to run another computer ethernet connection without any problems. I am sure that I could do the same with 2 cameras using external power to both.
Just trying to get a conversation started to see if this hack would be possible.... 
theoretically