Not a one size fits all question… Keep in mind, depending on your scale and env, devops may not be a full time job so if you hire a dedicated devops engineer, they may sit around doing nothing at times. At the same time when shit hits the fan, you don’t want to find your only devops engineer on vacation with no one else who understands anything. The problem is that devops can have a longer ramp than feature development since there are so many different flows/scripts/systems that need to be learned and understand which means more distractions if each engineer has equal input to devops work. Maybe hiring a person who is both part time DevOps and part time backend engineer may be a good compromise who is the owner for env configs, backups, etc. Combine this with some devops engineer rotation so you have redundant engineers that can be on call.
Don’t hire devops early. Tooling these days has become so good these days (docker, heroku, lambdas, etc.) that most competent full-stack engineers can figure out enough devops work to remove need for a dedicated person
Additionally, I think it’s an advantage to require the engineer who worked on a feature/service to be able to debug/triage deployment/ops issues