In Taoism, Jiang Yao is regarded as the ancestor of Tianshi, and his coming and going are mysterious. This shows that he has a lofty position in Taoism and is respected by many people.
But to evaluate whether a character is a good person or a bad person, many factors need to be considered, such as his behavior, words, thoughts and so on. Because we don't know Jiang Yao comprehensively, we can't make an accurate evaluation of him.
So there is no clear answer to this question.