Channel usage

Here's the full answer:  Due to how 802.11 works a router and a single satellites will not interfer with each other.  It's part of the spec that wifi devices on the same channel coordinate their transmissions. Since the APs need to be close enough to each other to have reliable communications for the backhaul to work they are close enough to coordinate.  However, it does nothing to benefit performance since only one AP in the pair can talk at a time to their respective clients.  Where this can become a problem is when you have multiple satellites and the satellites are far enough away from each other (for example on opposite sides of the router) that they cannot coordinate their transmissions.  Then you can have problems with two or more satellites transmitting at the same time causing interferrence with the router or clients who are inbetween.  Additionally you could have issues with clients who are too far away to coordinate with APs or clients other than the one they are associated with which can cause interferrence with other clients or APs.

Basically, using the same channels at best will cause a loss in performance, which is the reason why there is a separate backhaul channel to begin with.  At worse sharing channels will cause interferrence leading to packet loss.  On 2.4Ghz they might as well share channels since it's so crowded anyways but on 5Ghz there is no reason or valid excuse to doing so.