You will gain full miles, but no status or booking bonus miles. If you also have Delta miles, and the flights are available through their website (sometimes it's less expensive through the United Site then the Delta site, go figure), you may want to book it there for the bonus miles for booking online.

Any United Status will do you nothing in getting a decent seat on Delta, but Delta allows anybody to reserve an exit row if that is important to you at the time of booking (or they did).