Satan always wants his archangels to think that he has control over every situation that they embark upon. To hold a position of power as Satan does he needs to constantly be showing how everything yields to him and the cause he is fighting for. Satan is obtaining all of what he calls "these" from the deep.
The deliberate use of the word "yield" in referring to what the deep will give can have multiple implications. Milton could be using the word yield to show how much power Satan has over many things, especially his power over hell. Satan is not merely going to obtain "these" from the deep, but he is going to force the deep to yield them to him.
Another implication could be that of yielding a harvest. As I said in describing what "these" were previously I used the maxim of "sewing the seed." The deep is going to yield everything that Satan needs to sew his seed of evil throughout Heaven and everywhere else, thus destroying what is and reproducing things of darkness.