You can have the polygons in the head render with a different material, yes. How you do this depends on which DCC tool you use, but it should be possible to select certain polygons and assign a different shader in there. In this case, it sounds like you would want to select the UV islands for the head and assign those polygons a different shader. Unreal will respect this as a separate material slot on import.
From there, the materials can sample from the same UDIM set if that has already been created. The body material simply won’t sample the head UDIM tiles as it has no UVs in that space. The same is true in reverse for the head material. The virtual texture system should take care of this transparently.
Do be aware that two materials will increase the draw call count for the object as each draw can only render a single material.