Hello Pete,
The short answer is that you need the iOS Developer Enterprise account. This is required as our Native iOS App Center App (ACA) must be built with an iOS Developer Enterprise Distribution Certificate- it does not support a standard iOS Developer Distribution Certificate.
You can use App Center with just the default "web clip" ACA, but this has limited features and functionality in comparison to our Native iOS ACA. Also, app wrapping is not officially supported in conjunction with the web clip ACA.
So, in order to access full product functionality and feature set, an iOS Developer Enterprise account is required.
Let me know if this answers your question
Regards,
Andrew