How stable is the VMWare vCenter Server OVF and is there a better way to get HA features?

The Linux-based vCenter appliance works. It's a supported setup. You can run it as a VM virtualized within your cluster. Is it optimal? Meh. Is it used widely? Not in my experience...

There are also limitations surrounding the use of the appliance.

• No Update Manager (which can be useful)
• Embedded database, DB2, only supports 5 hosts and 50 VMs (you'd need an external Oracle instance to scale beyond that)
• Oracle is the only supported external database

I tend to think in terms of long-term stability and mindshare for support purposes. Most people run vCenter on Windows. As a result, guides, tuning recommendations and engineering knowledge are biased towards the Windows version.

Given the environment you're describing (hundreds of VM's, 5 hosts), you're probably planning to pay a lot for VMWare licensing, so the cost of a Windows server license shouldn't be the issue. I'd wager that the expertise and support options for your proposed VM infrastructure would point to using Windows over the Linux vCenter.