Another reason to use concave/dished pistons is that one usually want's to maximize the distance from the piston top to the first piston ring. On the other hand it's better to use long rods and have the pin higher up in the piston. So everything is a compromise. The black top has 3.0mm longer rod and the pin is 3.0mm higher in the piston. This is the reason not to mix and match.

On the other hand, if we are talking only hemi CVH heads, they don't really have any squish area at all. So I guess the LET pistons are ok for ZVH if the compression ratio is ok.