I don't think that would be the same ,, that would be more like a base coat.

primer is somewhat absorbent and leaves a finish that paint can grip to. also most primers sand very nicely.

 Depending on the paint,very thin paint will not sand near as well.

 not all is lost , a thin base coat has it's purposes as well and could substitute for primer in some cases.

and I have seen people using paint to bring out sanding marks and errors.Grendels for example check out his 747 build.