You wouldn’t want to setup RRAS on a domain controller, especially if you are multihoming the machine. Multihomed DCs are not recommended due to the numerous errors generated with DNS and the multiple names registered. Causes issues with AD.
You can do it without AD. It’s NOT required. Install it on a member server! Do not install RRAS on your DC – ESPECIALLY if you have multiple nics!
If you are using it for VPN, you can use the local machine’s user accounts to authenticate users, or if using for NAT, no problem. Even if you have AD, you would still want to put RRAS on a member server.