Are you asking about a VSAN zone merge versus an IVR zoneset merge?
VSAN merge rules are outlines in the T11 document titles FC-SW-5 available from the T11.org website. Section 6.1.15 contains all the information you need.
As for the IVR zoneset merge, basically the same rules apply, but only to devices that are online, and contained in the IVR zoneset on each end of the link that the merge is taking place across. IVR is Cisco proprietary, so the Cisco docs are the only reference you will find on that subject.
Hope this helps,
Mike
