Found an Internet Archive snapshot of the page at
http://hise.audio/manual/ios.php
which currently displays some error. There I found helpful information on the missing pieces:
- wasn't using the Xcode project generated at
Binaries/Builds/iOS/
- needed to add the Apple Team Development ID in the HISE User Settings and an App Group ID in the Project Settings
Now the same basic project, which I've previously built as a desktop standalone and -plugin application, runs on an iOS simulator and an iPhone device, which is quite amazing.