As of today, as mentioned in this link, if you create a ProForma user picker field and link it to a Jira user picker field that is filtering to specific groups, the ProForma user picker field ignores those constraints and lists all users, even allowing you to select a user that is not part of the group configured in the Jira field filter.

When linking a Jira field with constraints like this one, Proforma should follow the same.