You should be able to output only the Z aov as deep by selecting the "deepexr" option from the driver dropdown options beside the Z aov. This will create a new aovDriver node that's set to deepexr type and can be controlled separately from the scene's default driver node. You can access the new deepdriver node by either selecting the AOV node using the "Select AOV Node" option (under the little triangle icon at the corner) and then graphing it in Node Editor or you can simply use the "Select Driver" option under the same menu.
You can also create a new aov driver node manually from the node editor and connect its message attribute to the Z aov node's outputs[0].driver attribute.
Do note to turn off the tiled option on this new deep driver node as Nuke currently cannot read tiled deep exrs. Your main driver can still remain tiled. If you are using the "Append" option for the main driver then it may cause issues as you cannot mix tiled and non-tiled modes for using the append functionality.
Hope this helps.
