Apple Remote Desktop multiple ports on one address / ip
Solution 1:
I'm not specifically familiar with ARD, but in general Apple assumes one IP = one computer. You'll be less likely to have these kinds of compatibility and interoperability issues if you give each VM its own IP address by using "bridged" networking on ESXi instead of NAT.
Solution 2:
If you set the VM's up with Bridged network connections rather than NAT network connections they will all get different IP Addresses on the same subnet. Best way to do it.