There is a big difference between SMEs and experienced practitioners (EPs). SMEs are helpful in the creation of courses because their knowledge is realtively structured and easy to distill. You get content and theory from SMEs. EPs are helpful in the design of learning processes and in the implementation of learning because they have a wealth of practical experience and fuzzy tacit knowledge to draw on. You get context, relevance, and reality-focus from EPs.
I have used EPs very successfully as online instructors, particularly in reactive asynchronous or chatroom type modes where they add great value to the learning - I'd think twice about using them in ILT or Webcast modes.