If the guest lecturer is an expert in the field, the opportunity to participate in a lecture could be seen as a compliment, and the opportunity to promote their unique knowledge with a new generation of learners. We are in the final stages of developing our on-line learning courses (continuing education for those in our field - marine mammal training) and have a guest lecturer who is a scientist in the field. We plan to either video a lecture of hers or possibly have a live chat discussion as well. However, this is a relatively small field and we have close connections with the guest lecturers we are inviting. In a sense, you are right - during the guest lecture / chat, they ARE the instructor, and the students get the benefit of a different perspective, of one working in a specific related field.
