Can this app backup/restore RCS messages?

Yes it can, if you use Google’s Messages app for messaging.

Google’s Message app now supports RCS messaging with all service providers in USA as well as a lot of providers outside of USA. Messages stores these messages in the SMS/MMS database on the phone as MMS messages and SMS Backup & Restore can backup and restore these messages. If you wish to use RCS messages and backup/restore them using SMS Backup & Restore then we recommend using Google’s Messages app instead of the phone’s built-in messaging app.