This sounds highly unlikely. Last year, I accepted a VDB voucher from US Airways for giving up my seat. They put me on a Continental flight. I did not receive US Airways flight credit, but I did receive OnePass miles.

Actually, in another episode (also involving US Airways) my US Airways flight was cancelled and the gate agent put me on a Continental flight. I asked her about receiving Continental miles and she said that she would submit me to receive US Airways miles for my un-taken flight, and I could get Continental miles for the flight I actually took. In the end, I got my OnePass miles, but those US Airways miles never came to fruition.

In the end, I think that the airline who flies you will give you miles if another airline puts you there. I've never been in a situation where this didn't happen.