I checked with the SAS scheduling folks and this is what they told me:
The user needs writemetadata permission on the deployed flow object to schedule. This is usually done by having writemetadata permission to the folder containing the deployed flow.
The roles we generally use are:
Management Console: Advanced
Metadata Server: Operation
Metadata Server: User Administration
Metadata Server: Unrestricted
Metadata Server: Unrestricted is not required but the user, or developer in your case, will need to be given write metadata permission on the metadata server. In our testing environments this is most often done by adding the user to the SAS Administrators group. If this is not a viable option, then the user will need to be given write permissions on any folder(s) he will need to write to. In your case, perhaps a single folder can be created for the developer where he can be granted write permissions.
Hope this helps!