The simple answer is that it depends on what you mean.
Are emotions a source of knowledge? That is, is this an acceptable argument. Premise: I feel that X is true. Conclusion: X is true.
No, it is not, as emotion in itself has nothing to do with the truthfulness of any proposition. However, emotion may be a source of knowledge in a more implicit sense. Primarily so when it comes to making decisions about ethics, or what we should do with our lives. Emotion is an indication of our mental health state. We obviously want to be well, hence we desire a certain emotion. Only through an observation of emotion can we know what we truly want in life. Hence, our passions are something that needs to be analyzed from a dispassionate, objective standpoint. Although, they do not entail knowledge directly.