Yes, I'd like to know, too!
The Installation Guide indicates ESXi 5.1 & 5.5. However the KB tends to be updated with frequency.
Since they almost never use the wording (and later) I would tend to lean towards yes. When in doubt call support.
ESX 5 has had a good run with ePO as it supports 4.6,5.1 and 5.3.
Extra Info in case your interested. Found this on http://www.unixarena.com/2015/05/vmware-vsphere-6-0-vs-vsphere-5-x-difference.ht ml
In March 2015, VMware has released the much-awaited VMware vSphere 6.0 . Is it completely different from the previous VMware releases vSphere 5.5 and vSphere 5.1 ? No. The most of the features are remains same but there are lot of enhancement made on the existing features. For an example, VMware has brought lot improvements on the VM Fault tolerance in vSphere 6.0. Also there are few new features introduced in the VMware vSphere 6.0. Let’s see the new features of VMware vSphere 6.0. In the bottom of the article ,I have listed the differences between the vSphere 6.0 , vSphere 5.5 and vSphere 5.1 versions.
What’s New in VMware vSphere 6.0 ?
- VMware vSphere Virtual Volumes. (vvols)
- vSphere Content Library .
- Cross-vCenter Clone and Migration
- Increased Scalability
- Expanded Support
- Amazing Graphics with NVIDIA
- Instant 10x Faster Clone
- Network IO Control
- Multicast Snooping
- Multiple TCP/IP Stack for vMotion
- vMotion Enhancements (over distances of up to 100ms RTT. )
- Replication-Assisted vMotion
- Fault Tolerance (up to 4-vCPUs)
- Enhanced User Interface (web client)
Let’s see the comparison between VMware vSphere 6.0 and VMware vSphere 5.5 & 5.1 versions.
I called support and they said that they will only support those versions listed in the documentation. He said it will probably work in 6.0, but they won't support it.