👍 or 👎 ?

As an alternative, install JourneyMap and Xaero's Minimap on the server side. This will enable all their features natively.

How would this behave if your running the Fabric / Forge server behind a Velocity proxy, that has additional Paper / Spigot servers.

This plugin would still need to be on the Paper / Spigot and Velocity server, but how would the proxy behave when connecting to the Fabric / Forge server with their normal map mods.

You don't actually need MMC on the Velocity side, given that you can manually configure the plugin on the server side to use unique IDs.
And on the proxy side we just pass through anything that we don't understand, so it should work just fine with "normal" mods installed on the server.