This feature is available in all editions
I have project members who are not listed in the Sprint/Iteration Capacity grid. Why don't they show up?
The Sprint/Iteration Capacity grid lists all members and teams (if the Teams feature is enabled) who are owners of scheduled workitems (scheduled means assigned to a sprint/iteration).
To add a member, click the Add Member button. The Add Member list includes members assigned to the project who are not already displayed in the grid.
If you add a member, you must add at least one capacity value in order for the member to display in the grid.