Sauron, devoted servant of Melkor?

[Nilpaurion Felagund]

And Ar-Pharazôn said: "Who is this Lord of Darkness?"
Then...Sauron spoke to the King...saying: "...his name is Melkor..."

(The Silmarillion, Akallabêth - emphasis mine)

Sauron had more purpose for Morgoth outside Arda than in it. Very, very clever...

So still, Sauron wants Morgoth where he is, not running wild all over Middle-earth. It could very well wreck his plans.