Headless Mac mini: Share Screen + FileVault
Other answers here are correct - it is not possible to remotely access a freshly-booted Mac with FileVault enabled without physical access (FileVault operates 1 layer closer to actual software than a 'traditional' BIOS or firmware password).

It is, however, possible to remotely reboot a Mac and force it to allow remote access even with FileVault enabled, provided you issue the correct command:

sudo fdesetup authrestart


Apple calls this 'Authenticated Restart' official semi-documentation is available here, with a more in-depth view from C|Net gives a high-level description of its workings.

Note that if a Mac is not restarted with this command (a regular restart, powerloss, or otherwise), physical access will be needed to access the Mac. The command also (obviously) requires admin privileges to run.