A key defining quality of God is omnibenevolence. Therefore, it's impossible that an immoral command would issue from Him. Some may argue that this doesn't imply that God doesn't have a set of principles, and I agree with that. But the point is that God, being defined as omnibenevolent, only has to consult himself for moral decisions. In other words, God is morality itself, morality is not a set of principles separate from God according to DCT.
However, one could argue that if God is omnibenevolent and all that is considered good, then his moral commands would be defined as good as well. However, this would result in the statement "God commands good", turning into "God commands God". This makes no sense and is not a valid command.