Ansible is a configuration management tool and docker is a container runtime (am I getting the terminology right)? They can compliment each other and provide their individual strengths to many types of deployments. There is some overlap in how both tools and their larger ecosystems impact a system - but that’s not necessarily a bad thing.

I personally prefer a different setup, but any team that already has a strong skill set in both tools may benefit from building on top of preecisting domain knowledge.