Currently Field users are only allowed to status Resources when Resources are assigned to tasks. If it is RG assigned to tasks, user will not see any tasks displayed in the list therefore update status is not possible.

Improvement should be either R-task assignments or RG-task assignments (for WP users as RG is a concept of RG in Pro), query tasks and query R assignments to tasks directly through R-Task or indirectly through R--RG-Task.