Relation of devops with release management
Your use of the term "devops" suggests that you see it as a role.  I humbly suggest that developers that are part of a Scrum team aren't called "Agiles," so DevOps practitioners aren't "devops." :)

Release management is absolutely part of DevOps.  It's one of several specialty engineering roles.  Staffing for the skill of release management varies widely from one company to the next.  The size of the company, the industry, and the size of the IT department all influence how (and if) that skill is isolated to a person, a team, or distributed across IT.

Organizations of medium to large size tend to have dedicated staff that understand the practice and tooling of Continuous Integration.  This includes some systems admin skills, and increasingly includes development skills, at least scripting.  The growth of Infrastructure as Code as a practice is blurring the lines between release managers and developers.