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Tolkien does state that while Morgoth wanted to destroy Ea, reduce it to chaos, Sauron wanted absolute control - as we see in the War of the Ring, the people of the West are fighting to avoid becoming slaves, not to avoid becoming corpses.
This being the case, I'd say that the last thing Sauron would consider doing is releasing this being who wants to wreck his plans for world domination! Sauron would make use of the memory/idea of Morgoth - as in Numenor, & also of the remnants of his evil spread throughout Arda (the idea that the whole of Arda is Morgoth's 'Ring', the object that he pours his evil into) to make his own rise to power easier, but I think that's as far as it went. I don't think Sauron had any concept of loyalty!
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