Not anymore. It was removed in stretch, I think. The reason is that systemd won't let you into single-user mode if the root password is unset.

edit: If, after installing, you install sudo and manually disable the root password, you won't be able to boot to the rescue or emergency targets; a valid root password is now required by default.

If you want them to work without a password, like classic "single-user mode", you can edit both the rescue and emergency unit files, and add the --force flag to sulogin.