I'm having an issue whereby if any of my windows VM's are up and running when the server is put to sleep the disk becomes corrupted. (I realise sleep is not supported). The issue presents itself as a VM that takes an enormously long time to boot.  Sometimes booting into safemode, and running check disk fixes it. Usually I'm restoring it from a backup.

I don't believe sleep it's really supported for a kvm server. It's designed to run on a 24/7 server. You will need a script to shut them down on suspend and restart on resume. Not sure but you might be able to suspend the vm's then suspend server. I would try that first and see if that works.