My favorite, and IMHO the best spin instructors at my gym, are also cyclists. I think this is because they are more focused on fitness results through interval training and such rather than an hour-long stream of pure cardio and cheerleading/drill sargent hollers. I also know they get better results from their new spinners, even, or especially those with a lot of weight to lose. The very best instructor is a champion masters road and track racer who often teaches off the bike. He can walk around, check your HR, offer tips/encouragement, refill your water bottle, etc. He observes his spinners carefully and seems to have a clear idea of their status and improvement. His class are almost always full.
The non-cyclist spin instructors more often come in, jump on the bike, ride like maniacs for an hour, and go. Some people prefer them, I guess, but when I must take one of their classes, I ignore or modify their routines (push ups on the handle bars while doing high-cadence? how about I spin and then do real push ups on the floor, instead?)
I think of all the trainers at the gym, the spin instructors have the best opportunity to take unfit people under their wing and help them get real results. So I say, please go for it! Confront those front-of-the-room jitters (DH and I both did in the educational world and are now considered classroom naturals, hoho) and help people change their lives!