To hide a group Shift+Ctrl+Click on it - this hides all but the group. Then Shift+Ctrl+click on it again - this reverses the visibility so that all but the group is visible. To show the whole of the mesh Shift+Ctrl+Click on the background. Also remember that you can use the Tool>Polygroups>Group Visible to adjust grouping.
But from your question it sounds like you have separate meshes laying on top of one another. If this is the case, then export each mesh separately as an obj from Maya/Max. Then import each individual .obj into zbrush. This separates them into their own subtool which act like layers if you will.
edit: You can also use the Tool>Subtool>Groups Split to separate each mesh into its own subtool.
Also if you just want to paint, not sculpt, make sure RGB is turned on and Zadd/Zsub is off. You can also hide the polygroup, mask all, unhide so you can still see it but have it 'locked'
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But from your question it sounds like you have separate meshes laying on top of one another. If this is the case, then export each mesh separately as an obj from Maya/Max. Then import each individual .obj into zbrush. This separates them into their own subtool which act like layers if you will.
edit: You can also use the Tool>Subtool>Groups Split to separate each mesh into its own subtool.