You can physically install and download on as many machines as you want. The licence does not allow this though and it is likely an enterprise licence that he is breaking the terms of, or a single user licence for multiple machines.
You cannot register as the serial number will be linked to his support account. When VMWare notice that he suddenly has 200 installs all over the world, it will likely block the serial number and suspend his account. You won’t be able to get updates, but it will likely keep working. You won’t be able get the reduced upgrade.
So yes dodgy, but will likely provide a working environment. If you genuinely need VMWare Pro, you can probably justify the license cost.