Sauron and Gollum

[Raynor]

Did he even know Gollum was captured?

He apparently did:

Originally Posted by The hunt for the ring, UT

Now Sauron learning of the capture of Gollum by the chiefs of his enemies was in great haste and fear

And seeing that in the Council of Elrond it is stated that the attack on Mirkwood was previously planned and it had as a purpose the "release" of Gollum, of which he knew, I would say that Sauron was behind that attack too, directly or through the nazgul.