System administrator permissions are not required for Fusion development. What Fusion can do will be limited to whatever the user account that Fusion is using is able to do and see. For example, if the user account cannot see some projects in Workfront, then they won't be able to see them in Fusion. This applies for most objects in Workfront. The one place I have found it doesn't apply is in the list of fields when configuring a Workfront module. Whether a user has permission to see a field or not, it will still show up in the pick list.
One thing to highlight, is that if there are forms with fields in an admin-only editable section, then system administrators are the only users that can populate those fields, so a non-sys admin Fusion user also wouldn't be ablet to populate those.
