Currently the user interface to manage fields on the data tab is not available for members in a shared update group, it is only available to the owner for the feature layer. The members have the ability to add fields in the attribute table in the map viewer and through the Admin API using update definition and I would imagine they can do this in Pro as well. However we have a shared update group where we want members to be able to add fields and also update domains for fields. These users do not always have Pro and would not have the technical knowledge to update JSON using the Admin API.
