I have not. DRC and Rwanda have this agreement where former FDLR from Congo are being demobilized and sent back to Rwanda, where they go through a re-education process and try to reintegrate.
I have not heard of people in Rwanda leaving Rwanda to go to the DRC to fight, but we have heard of people from Burundi leaving Burundi to fight in RED-Tabara and Forebu, which are armed groups specifically linked to the Burundian crisis.
What you are mentioning could be true, but I haven't seen evidence of it or reports.