Presumably they wouldn’t necessarily know the 2nd server even exists if they’re just hitting the reverse proxy. As long as both the reverse proxy and the origin server aren’t under the same VPS provider I would expect that to be fine.
Reverse proxy gets targeted, shut down, you spin up a new one somewhere else and keep going.
$10/m for 1 provider and 1 indexer?
If you hunt around this black friday you should be able to get a better deal than that. For reference I have 1 unlimited provider (newshosting) for about $30/yr and 2 indexers each around $15/yr