Assuming you mean the Miller pocket is tighter than the Warmoth neck heel width by an amount less than 1/16", it should.
Different pieces of wood, different species, from different places are bound to shrink or swell differently merely from existing in normal/typical environments. Now matter how precisely cut (using CNC machines) the neck pocket and neck heel I've never had neck pocket and neck heel fit well without at least a little bit of sanding the walls of the pocket. In other words, seems within normal range.
It's better to start with a neck pocket that's a tiny bit too tight than one that's too big because carefully removing a tiny amount of material is easier than adding material.
