Is it OK to mix operating systems in a multi-node Zimbra environment?

I am moving from some old hosts running RHEL5 to VMs running Ubuntu 12.04. Both are 64 bit. Can I add new Ubuntu 12.04 mailbox VMs to the existing RHEL5 I can migrate accounts to my new VMs? I'm eventually going to migrate all the MTA and LDAP nodes to new VMs running Ubuntu 12.04 as well.

Just curious....