It looks like we have to decide which Satan we are talking about. As Chai Tea noted, there is the Biblical Satan and the, I'll call it, pop-culture Satan build up in medieval and modern times.
It has been said in this thread that the Biblical Satan does not control or punish anyone. However, in the passage that Questioner quoted (Revelation 20:7), Satan is "loosed" upon the world so as to deceive it and turn it against God. Well, loosed by who and why specifically in 1,000 years? It sounds like it is part of a plan, maybe God's plan? In which case God seems to have decided to use Satan as a test of humankind in the end of days. Was this in God's plan from the outset? I think not as the Angels were also invested with Free Will and it seems that Free Will is always messing with God's plan. So it seems God is using Satan in Revelations 20 as a sort of amendment to how he might have wished things to go (naked people dancing around eating figs and lettuce in Eden). Why would God unleash Satan upon his children? I will argue it is to test Free Will.
Free Will seems to be a black box to God in that He is never quite sure if we really love him or are being faithful to Him in our hearts. By testing us, he is reassured, apparently. God tests many of the prophets to insure their loyalty as it seems he can not know for sure without some outward gesture. When God tests the prophets, or anyone, the Bible does not call God's test Evil. Even asking for the sacrifice of ones child is not seen as Evil (the psychological effects of actually having decided to kill your child is not something I would want to endure). So when God uses Satan, who seems to be firmly in control of the Biblical God, it should not be considered Evil.
Now the question originally was, is Satan himself good? The Biblical Satan seems to be bent of the overthrow of God. I have not seen anything depicting Satan as being against humanity. In fact, it was Satan who gave us the knowledge of Good and Evil and he may have given us everlasting life had not God immediately protected that tree with the fiery sword that swings in all directions. The Bible is pretty clear that it is in fact God who has prepared hell for humanity and Satan and the fallen angels.
So I'm not exactly sure what to think yet about the Biblical Satan and am very interested in what people have been saying and hope that people continue to share their thoughts.
The pop-culture Satan seems a bit more clear cut to me. This Satan is in charge of hell and all the wicked people go to hell. The books are opened in Heaven and the righteous pass into Heaven and the wicked fall to hell. Again, no good people go to hell. So based solely on this, Satan is working for good.
Pop-culture Satan also tempts the living with wealth and fame etc. This is again testing free will. The question is, without these tests would everyone get into Heaven. What is it in a persons heart that causes them to sin? Would they sin without Satan? Would they express the corruption of their Free Will given non Satan inspired opportunities? I will argue yes, based on the tests God found it necessary to inflict on the prophets in the Bible. People will sin and turn from God even without Satans help. It seems that Satan is doing us all a favor be weeding out those whos hearts are not perfectly true in their alignment with God. Satan has no power over the righteous, only those who choose to sin. So as long as he does not harm the righteous, Satan can claim at least a neutral outcome here. I would even say he is working for good, but I won't push it.
Now there is this little nagging bit about Justice. I'm going to use Plato's definition of justice here, in which case Satan is not about Justice. But then God is not about Justice either, as I noted above, eternal punishment can not be Just. So I'll give God +1 Evil and Satan +1 Evil = neutral.
My thoughts so far...
Kind Regards