Yes, I have a shift kit on this build. However, the pivot point of the swingarm on this bike is in front of the crank axle, which means that the rear suspension does affect the tension of the chain that connects the jackshaft(shift kit) to the main chain ring. I do not use a tensioner, but keep this chain tight. I do not have any issues with it at all.
I did have the bike for a couple months without th shift kit. In this configuration, the rear suspension affects the tension of the main drive chain. I used the stock tensioner and didnt have any problems, but I didnt ride it enough to be able to say with certainty that that is reliable. Im making another bike now with this frame, which will not have a shift kit, so Ill chime back in here and let people know if they are interested in how that turns out.