I think it's a legitimate question... Anyway, yes to all three. We still run some CentOS 5 VMs on newer SL6/CentOS6 hardware nodes without any problems.
All of our CentOS 5 VMs have been freshly recreated, though. I'm pointing this out because there have been some reports about instability when using old VMs (ie. created on HN with Red hat 5 openvz kernels) that were transferred to newer HN (RH 6 kernels). YMMV... I'd search for such posts on the forum, mailing list archives and bugzilla to see what you might expect if you go this route.