If you accept the UA routing you'll get original routing credit from Delta and you can credit the full Y UA ticket to your favorite Star Alliance program.
I was rebooked on NH a couple of months ago. I already got ORC from Delta, but you are saying I can have ANA credit me for that flight?!
Edit: Yes!! It worked!! I just did the retroactive mileage request on ANA's site with no problem. It asks for a 13 digit ticket number but make sure you enter the entire number.