Hi,
Q1: If I install ROS x86 on vmware and license it, can I move safely this installation to another vmware machine?
Q2: (provided that A1 was “Yes”) Can I move this installation between an ESXi instance and non-ESXi instance?
Thank you in advance.
You can even copy the machines and you will not loose licence. Just try it. You don’t risk anything. I don’t know the second answer.
AFAIK, the license is bound to the HDD, plus you can copy the HDD file. So… as long as that’s present, yes. You should be able to make multiple different sorts of VMs, and attach a copy of the HDD to them.
Technically, as long as the virtual disk does not change (*), licence will work. Even multiple copies would work, but I’m sure that it’s not how MikroTik meant it. No “buy one and then use hundered clones”. 
(*) It does not depend only on the disk content itself. I had no problem moving ROS VM between ESXi and VMware Player. But moving the disk from VMware to VirtualBox, even though it also supports .vmdk disks and it did not change, did not work, softid changed.