Some outer tie rods come with a grease fitting, which often come pre-greased and do not require any additional grease added when installed. However, make sure the grease fitting bolt is tightened during installation.

Should new outer tie rods be greased?

Modern tie-rod end do not require grease. The clearances are so tight and the surfaces so smooth that additional lubrication is unnecessary. As for the ring you're probably right about it just holding the boot in place, which is necessary to keep crud out of the unit and prematurely killing it.

Do MOOG outer tie rod ends come greased?

While MOOG greaseable parts come greased from the factory, they should also be greased at the time of installation to fill the dust boot and lubricate the interface between the boot and mating part.