Running an ultramarathon is considered to be extremely demanding. Unless the regular OOTYULTRA no pre-qualification is required to participate in the virtual ultramarathon. If you are not a regular ultramarathon runner (esp. the 60k & 90k distances), you can complete the chosen category during the 4 days event window.
However, it is highly recommended that you are aware of the physical / mental demands and choose your running category matching your potential.