Not that I expected it to work, but I did just confirm that Casper does not work with El Capitain beta 1. With the new security settings on OS X, /usr/sbin (along with a number of other system directories) are now read-only, even for root. I haven't tested installing with the new security restrictions disabled yet, right now I'm just trying to figure out what isn't working.
At least I'm completely confident JAMF will have an update out for us when El Capitain ships this Fall, unlike some other vendors I have to deal with...

