Can non members speak in Sacrament Meeting?
Thanks for your question. In describing sacrament meetings, Handbook 2 states:
Selecting and Orienting Participants
Selecting Participants. The bishopric selects members to participate in sacrament meetings.
After the sacrament, the bishopric member who is conducting the meeting bears a brief testimony. He then invites members to bear heartfelt testimonies and to relate faith-promoting experiences.
However, I have witnessed several occasions when non-members address the congregation and even bear testimony. I have never seen a bishop prohibit this behavior. So while it is non-standard for non-members to bear testimony and not encouraged, I do not believe it is prohibited. Such a decision would be at the discretion of the bishop or other presiding authority in a fast and testimony meeting.