The system has an NVDIMM module that contains any uncommitted writes. Its contents are also mirrored to the NVDIMM in the standby controller. NVDIMM is a combination of supercapacitor backed DRAM and Flash memory. In the event of a power outage, the contents of the DRAM are destaged to the flash component of the module. You don't have the traditional time limit of a few days to restore power. It is persistent storage. When you power up the system again, any writes in the NVDIMM will be destaged to disk.
A graceful shutdown might have the minor advantage that the subsequent startup could be a little faster but your data is protected either way.
If you really want to ensure a clean shutdown, how about a script to connect to the array and power it down after all the servers have been shut down?