I work with a company. We have a UX team that is separate from the developers (which won't be changing, so we have worked out methods to collaborate with developers). To be honest, I would not say that we are using Agile even though Kanban has been introduced. The Kanban board is useful, but people are treating it more like a calendar than something that helps to manage the process and they constantly ignore the WIP limits. As for ownership, usually whoever started the project on the business side acts as its owner. However, we also find ourselves answering to other people along the way, and it often escalates the scope. A lot of the problem is, in fact, the project process. Business requirements, scope, and a roadmaps are not often planned. Often things are simply mandated down the line. Or, if we are brought into the project planning, stakeholders tell us they don't have time for UX.
So this is largely a matter of culture change and project process change. The thing is, I'm not sure what techniques to use to persuade people or guide the project process in a better direction.