I'm using field_permission to hide fields to users without proper role and this brought a fieldset to be empty for certain users.
BTW the fieldset itself is shown even with no fields in it.
I think should check that user could see at least one field before rendering a fieldset.
I had a look at the module code, and I've seen there's a function called
field_group_field_group_is_empty, but it just checks if a group has children, not if user can see them.