God is not the author of evil. The Hebrew translation of "evil" in the scripture you quoted is adversity or calamity. There are two forms of the word: moral evil and calamity or distress. The KJV often refers to adversity or calamity.It's a bit more complicated than that,"I form the light, and create darkness: I make peace, and create evil: I the LORD do all these things" (Isa 45:7 KJV)
"The LORD hath made all things for himself: yea, even the wicked for the day of evil" (Prov 16:4 KJV)
"Shall a trumpet be blown in the city, and the people not be afraid? shall there be evil in a city, and the LORD hath not done it?" (Amos 3:6 KJV).
In the old testament and prophets, God does a lot of unique things. Mind you, I don't believe these are literal events, I see it all as symbolic, for something more internal, to me the bible and stuff, are psychology books of their time. thats just my opinion.
anyways in answer to the question, I don't know. It depends on how one defines Good and how they see a demon? No one is good, but we all seek to do according to our concept of good, which figures its way by influence which comes to us from those outside, what we are educated with... that then becomes uniquely mixed with our own thinking and experiences. I can't see I believe in morality, only as an ideal. So as a result, a person is both bad and good, demon and angel, wolf and sheep. What we want to be, it is difficult to be, often we want to be good, but we fail short. Are behaviorism is predictable, given the stimulus, and we seem to experience the same type of stimulus, same type of associations daily. So for a human it is even difficult to be good, in the gospel, Jesus suggests that not even he was, only God was. Plato, through Socrates wrote about The Good, and the ascent to it, was not something already man in us, but something that takes layers of working through to in order to reach, as an Idea, much less and ideal. The Good, symbolized in the sun, an objective source of Light and heat, which shines on everything, despite its nature or formation. So can a demon be good? Well the devil is good, the Antagonist is what moves the progression of the protagonist, to manifest fully all the qualities that is potential in within. The hero is developed by the villain, without the villain, there would be no ultimate good, there could be no growth. The antagonist is a force of resistance and it is between the compelling force and the resistance force, that a new quality can be build. So I guess, a demon can't be good, for it has to be what it is, but its existence brings about the greater Good. Greater good taken differently, as than ordinary good, which is the opposite of bad. This is consistent with Judaism and the gospel honestly... although likewise consistent with the yin yang, perhaps even zen... i dunno.
This reminds me of an old Gnostic piece of literature, I believe the Phillip Gospel,
Light and Darkness, life and death, right and left, are brothers of one another. They are inseparable. Because of this neither are the good good, nor evil evil, nor is life life, nor death death