Is registry restored after a system restore?

Yes, system restore keeps and restores backup copies of the registry.

In fact, the registry backups can be used without system restore if your system has a corrupt registry. They are stored in the "c:\system volume information" folder.

Microsoft documents the procedure to restore just the registry manually here: https://support.microsoft.com/en-us/help/322756/how-to-back-up-and-restore-the-registry-in-windows