Short answer: It depends on the HRA type. A traditional/integrated HRA covers employees enrolled in the group plan; ICHRAs can be offered to all employees or defined classes; and QSEHRAs must generally be offered to all full-time employees on the same terms.
HRA eligibility follows the design. A traditional (integrated) HRA must be paired with the employer’s group plan, so only enrolled employees qualify. An ICHRA can be offered to everyone or to specific permitted classes, but not as a choice against the group plan for the same class. A QSEHRA, available only to small employers without a group plan, must be offered to all full-time employees on the same terms. In every case, nondiscrimination rules limit favoring highly compensated employees.