I zero seperately and then check. If they align I'm good to go. So far they've always aligned, so I'm not sure what I'd do if they didn't.

I tend to use "co-witness" to verify that the sights and dot are both still zeroed. If I pick up the gun and look through the iron sights and optic at the same time and find that they line up, chances are about one in a million that they both got knocked out of alignment to the exact same point.

At the end of the day though I'm not sure that it matters what you call it or what you use it for as that's really just a matter of semantics and personal preference.