The G7 has a Westmere generation CPU, the Gen9 has a Haswell generation CPU.
vMotion requires you have the same subset of common CPU instruction sets and features on source and destination CPU and enabled in the server's BIOS.
That means in your case:
You will be able to vMotion a VM that was powered-on on the G7 host (VM is running with Westmere instructions) to the Gen9 and back as well (but only if you haven't re-power cycled the VM on the G9 host).
But you will not be able to vMotion a VM that was powered-on on the Gen9 host (VM is running with Haswell instructions) to the older G7 host since it lacks these newer CPU instruction sets.
This is where EVC comes in. By enabling EVC on the cluster with the lowest common CPU generation (in your case Westmere), all hosts will present only these instruction sets to VMs when they're powered-on, which makes live migration possible across different physical CPU generations.
See these articles for details on EVC:
Alternatively you could also manually mask CPU instructions per-VM with advanced settings if you don't have source and destination host in the same cluster, but it's a tedious task and I wouldn't recommend it.
Thank you very much for the explanation!
Meanwhile, I also found the EVC.
But I found no evidence of the required licensing for EVC.
Is VMware Standard enough or I need the Enterprise Version?
Thank you again and have a nice weekend...
EVC is available for all licensed versions that include vMotion, so, it's available for Standard license as well.