Your question is unclear.
1. The OS name and version number you mention are inconsistent. Do you mean "Mac OS X Leopard 10.5.8", or "OS X Mountain Lion 10.8.5"?
2. Are you asking about using Leopard (or Mountain Lion) as the host OS or the guest OS?
If you mean you want to run VMware Fusion on either of those versions as a host OS, then VMware Fusion 8.5 won't work because it requires a later system.
For Mac OS X Leopard 10.5.8 as the host OS, you need VMware Fusion 3.x or earlier. (The Mac must also have an Intel processor - you can't run VMware Fusion on a PowerPC Mac.)
For OS X Mountain Lion 10.8.5 as the host OS, you need VMware Fusion 5.x, 6.x or 7.x.
VMware Fusion licence keys are tied to the major version number, so you would need a different licence key to use an older major version of VMware Fusion. The question is whether VMware Support can still issue licence keys for versions that far back. If you want to keep using VMware Fusion 8.5 you will probably need to purchase a second license and get it downgraded.
On the other hand, running either Leopard or Mountain Lion as the guest OS is possible in VMware Fusion 8.5 without any VMware licensing issues. Leopard must be the Server edition, as the standard (client) edition is not licensed for use in a virtual machine.
