I have a question with regards to using multiple distinct CobraNet VLANs within a Nion project. As I understand it a group of NioNodes interconnected via XDAB elect a clock master, that master unit in turn uses its CM-1 as the clock source. Say for example I have two Nions XDAB'ed together, but each of their Cobranet interfaces are on different VLANs, which means the clock reference on the XDAB may not be in sync with that unit's CM-1. In cases like this, is it a requirement that each of these NioNodes act as the Conductor for the CobraNet VLAN to which it is connected?

Note exactly, although it is recommended.  You could have one be a CobraNet slave, as long as it is also the XDAB master.  The second unit would need to be a conductor.  However, best practice would be for all the NIONs in the XDAB cluster to be CobraNet conductors.  This would provide the cleanest and simplest clocking path.