My understanding is that pretty much every modern init system has a service for mounting the devtmpfs, even if it's not in the fstab, and depending on the switch_root binary being used, mounts made in the initramfs may or may not be re-mounted in the new root.

You don't even need a devtmpfs in the initramfs environment, and it may or may not even persist into the fully booted system. I believe Systemd has a tmpfs unit file, and OpenRC has a service for it which is enabled by default.