Hey Melmaninga,
I have heard confirmation that conversely, DS doesn’t mind being symlinked to a package store, so that might be worth giving a shot. And to extend it even further, modifying your instaUp2Date catalog files to instead make reference to the URL’s in your munki repository can save you concerns about which is the authoritative source, since instaDMG would conceivably be used less frequently and just cache whats being distributed by munki. Hope that helps,
Allister