Should I neck turn Lapua 6.5 Creedmoor brass for a no turn Sami chamber?

No. For the size of targets we generally shoot at, neck turning is a complete waste of time (and doesn't necessarily guarantee an increase in accuracy).
 
I turn necks, but only because I have a tight neck chamber. If a loaded round would chamber without turning, I wouldn't bother. If my brass had inconsistent neck wall thickness, I would get new brass. I believe that if your neck is uneven, the entire case has uneven thickness.