I once saw an engineer deploy 3 CUCM publishers on a single 8-core host, each with 4 vCPUs. The math looked fine (12 vCPUs on 8 cores? Not fine). Call quality degraded during peak hours. TAC refused support until the VMs were moved to dedicated hardware.
When in doubt:
Cisco CUCM Virtualization Requirements: Architecture, Sizing, and Best Practices cisco cucm virtualization requirements