Can physical and virtual graylog-server machines co-exist in the same cluster?

I’m having problems sustaining a message arrival rate of over 80,000 message per minute with my OVA based graylog-servers. I cannot get the Citrix ADC to balance across three graylog-servers with 24 vCPU’s each using the available settings.
I’m trying to test a physical server with graylog-server in a cluster only containing OVA based graylog-servers.
Is this possible ?
If so what considerations are there ?
Can the graylog-servers be at different major levels (i.e 2.x)

Yes, that’s perfectly possible.

The OVA was designed for demonstration purposes and to implement POCs and similar small setups. If you’re running a larger Graylog cluster in production, I’d recommend setting things up properly, e. g. by using the Chef cookbook or the Puppet module.

No, they have to have the same version (e. g. all 2.1.x or all 2.2.x).