I would bookmark this page for future reference. Cisco Collaboration Virtualization. Looking on there for CUCM and then version 9.1 I believe it would be supported as I think the versions listed are minimums for each particular version of ESXi
Co-residency support= Full
Supported Versions of VMware vSphere ESXi= 4.0 U3, 4.1 U1, 5.0, 5.1, 5.5, and 6.0
Click for "IOPS"