Yes, I'm sure because I could not install Snapchat without modifying the OSMinimumVersion attribute in the IPA plist file.
I could force the snap to be installed only by modifying the plist file, but it would still not work with App Admin :
The App Store will not show the Snapchat App in the Purchases tab, which is the only location where the Downgrade menu works.
It would work only if I had it installed with App Store but the App Store doesn't even let you try to download it if you don't have iOS 9.0 or newer.
So I really can't use App Admin on iOS 7