It is, unless you're just trying to use an off the shelf distro as your initramfs and that distro's default init choice makes the assumption that the kernel will mount devtmpfs for it.
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.
In this case, my point is for a system where the "fully booted" state is still within an initramfs. There is no "new root" past the initramfs, it IS the rootfs which will run forever until the system is rebooted or shutdown.