Can LaunchDaemons spin up after this initial unlock? I'm trying to get my Mac Mini server to run things regardless of my login status. It would be great to get FileVault enabled on the server with this. I'm OK to manually login whenever the power goes out.

LaunchDaemons don't rely on GUI login state so they should come up. If you use LaunchAgents then they won't start this way, but LaunchDaemons should be enabled once the data volume is unlocked and booting finishes.