From my Experience, since UC moved to Virtualized environment the gracefull shutdown of the UC Vms is not very reliable, you can use APC PCNS VM solution to try to gracefully shutdown the Vms on a BE6k. I don't think you will run into "unsupported" issues. However if by any chance PCNS shuts down the machines un-cleanlly which may cause system issues then TAC man not support you.
The issue with PCNS on a VM on BE6K is the following:
1 - If you have hardware/Software failures on the UCS server the Esxi hypervisor sometimes may just freezes so it will not proceed with the clean shutdown since the PCNS is also a VM which co-exists with within the Esxi Hypervisor
2 - Even if there are not issues with the Hardware , it may happen that the CUCM when commanded to gracefully shutdown it will not do to a hug process, when this happens it will request confirmation on the shutdown, if none is given the VM will not shutdown, if PCNS forces the shutdown in this situation , the VM will shutdown un-cleanly and therefore may corrupt the file system.
Regarding the CIMC which resides on the UCS some versions have a power management option which allow a graceful shutdown of the server if you have a redundant PSU, and 1 of the PSUs is not provided power (so no need of very complex integrations here, pic bellow). however also in this case if the VM is not able to preform a graceful shutdown because of a hung process the shutdown will unclean and it may generate a corrupt filesystem.
in CIMC you can use the Power Supply Redundancy Lost Filter
However if the possibility of an un-clean shutdown of VMs is not a problem I have found that the UPS PCNS or CIMC option are valid.