This varies from airline to airline, and often from situation to situation and/or person to person within a given airline.

It helps if the agent who reroutes you makes a note in your PNR that you should receive ORC. Customer Service, or whatever DL/NW call it, can see the note when you ask for ORC. In the specific case you describe, you can tell CS it was part of the bump compensation agreed to at the time, and without it you would not have taken the bump.

Receiving credit on both airlines: you can often get it, though the rules say "no," because you'll already have credit on the airline you flew and the airline you want ORC from won't know this. In your case it may be a problem, because you want DL credit for both and DL CS will be able to see that you already got credit for what you flew. The most you're likely to get is the extra miles for your original, longer routing. If you want to try double-dipping, go for ORC on NW or split them up some other way.

The ethics of this have been discussed here ad nauseum. Some say this is unethical. Others say it's fair compensation for the inconvenience. You won't find a consensus.