Converting Horizontal Activites to Agile Mode

Do you have reason to believe it would align at all? How would a "horizontal team" develop a useful, feature complete, integrated, and potentially releasable increment? Would they have the necessary range of skills to do so?

It depends :-)

Is Performance testing part of your DoD? Do you need the test data for making your Increment potentially releasable?

I can think of two options -

1. Members of Performance, Test Data management team should become part of individual Scrum team and they should work along with their Dev Team members for completing all performance and test data work every Sprint.

2. Keep them out of Scrum and they should get into action whenever they receive a request from a Scrum team.

I agree. The point is that with Organizations moving towards Agile, how will the horizontal teams get aligned with them - being a part of Sprints, How they would handle the requests received from Sprints and so on.

The member of horizontal team who is assigned to Scrum team will need to attend all Scrum events and commit to the story assigned to him/her during Sprint Planning. He need not be full time member dedicated to that project scrum team and can be part of multiple project scrum teams, but it is important that he commits to the stories and work closely with the team in order to meet the sprint goal.