Does the tension on both the top and bottom part of the chain need to be constant in order for cuts to be accurate?
No, you want less tension on the slack end of the chain than on the end
connected to the sled.
what I mean is, if the tension on the slack end of the chain changes, will that throw off the accuracy?
not as long as there is more tension on the sled side, that will keep the gears
against one side and you don’t have any backlash to worry about. If the tension
on the slack side gets higher than on the sled side, the motor will move without
the sprocket turning and you will have error show up.