Thank you all for your input. I did get the opportunity to discuss it with Allen Bradley as well. They did say it could be done with one sensor, but the second amplifier would have to be geared 1 to 1 and provide a mark of some kind to verify the 2 servos were parallel. They also suggested I monitor the current from each amplifier and make sure they produced close to the same value. If the value got too far from each other, there is the likely hood one motor was leading or lagging behind the other.
Saying all of this, they did suggest the best solution would to add a second sensor. When homing, move the (A servo) in to home while (B servo) is a slave. Move back a few inches, switch master and slave and home the other servo completing the homing procedure.