Wouldn't surprise me. I mean, DSPs wouldn't be able to scan packages to pick them up without being able to access the flex app, so unless there's a procedure in place to allow packages to be picked up and manually marked as having been picked up... they wouldn't be able to do anything. Moreover, even if they could pick anything up, they wouldn't have any way to navigate, drop packages off, snap photos, and otherwise record all that offline for later upload... because drivers probably can't even sign in.
What's worse, though, is that this also implies that even if an outage is localized to a particular region, data for deliveries to that region isn't multihomed, so you can't just failover flex app service to another region and keep delivering. For a service that lives and dies on being able to deliver everything faster than everyone else... that seems like a massive oversight... but also completely in-character for Amazon.