VMware's current guest compatibility list doesn't go back that far because Fusion 8.5 being no longer supported. It does indicate that Fusion 10 and later do support Windows Server 2012.
I did happen to find a hidden release note for Fusion 8.5 that indicates Windows Server 2016 support was introduced in that release. Because of that, I'd suspect that Windows Server 2012 would also run.
Also see http://partnerweb.vmware.com/GOSIG/Windows_Server_2012.html for information on using Windows Server 2012 as a guest in VMware products. It doesn't appear like there are any specific gotchas for using it.
As far as other gotchas, I'd be concerned from a security point of view
- Fusion 8.5 hasn't received any security updates in 6 years
- macOS High Sierra hasn't gotten any security updates in over 3 years
- Windows Server 2012 is no longer getting any updates except if you pay Microsoft for Extended Security Updates.
I'd only run this environment in an isolated network with no Internet connectivity. If you need Internet connectivity I'd recommend running that Windows Server VM on a Mac/Fusion combo where security updates are still available.