Technically, no. Part 61 only requires a 3rd class medical to instruct, regardless of the certification or rating sought. Now, what kind of medical do you need to get paid as an instructor? You'd think at least a second class, right? This was my understanding until recently. Apparently, the FAA feels that you, as an instructor, are being paid to instruct, not to fly. Now keep in mind, if you operated as a CFI with only a 3rd class medical, you would be limited as to what you could do (ie. no scenic flights, no photo flights, etc.) Lastly, to muddy the waters even further, if the student can act as PIC, you don't need a medical at all to instruct.