Bottom line, I think it would be a mistake to rely on
ICMP echo
requests/response for proof that a gateway is there or not. Our local
repeater coordinating body requires coordination holders to update their
record once every two years (or maybe it's three years). It's as simple as
logging in and clicking a button indicating that their information is
current. The database sends automated reminder emails when the update is
due. It has worked well for many years and is not onerous for the
administrative/system staff or the repeater owners. Something similar seems
like the way to go.
This is indeed how the portal currently works.
Chris