From ZFS 7320C point of view if the 7320 is configured properly with IP address as cluster resource then if one of the controller fails the IP will be taken over by other remaining controller.
For Oracle RAC queries there may be various aspects involved and you may contact relevant forum or open SR for details.
It's not supported.
* A Sun ZFS Storage Appliance NAS device must be directly connected (through the same subnet) to all nodes of the cluster.
It's possible only with switch.
1- If a controller of the ZFS7320C fails, will the remaining controller import the IP address of the failed one ?
Yes. But you configure IP address on both nodes for same interface.
( You can't configure IP1 on node0 net0 and IP2 on node1 net0.
After configure net0 on node0, This interface will be unavailable for configuration on node1 ).
2. Will ORACLE RAC keep working with the 50 seconds delay for the ZFS controller fail-over ?
It think it's will look like frosen databse.
3- Will ORACLE RAC "known" how to use a different Ethernet port to reach the dNFS volumes ?