Been doing vSphere since version 3.x, it has never encountered to me there was a limit in that space.
Having said that, there is a case where a customer would need this. Example, to have the VM name similar to the FQDN especially true in a multi-domain or tenant environment where VM name could be the same and only the domain or tenant is the differentiator.
So doing a quick check here is the below KBs that state the limit:
- As of vCenter Server 4.1, the number of characters support is 80. KB
- Display names for any objects e.g. VM Name, Datastore Name, etc. should not contain special characters like %, &, *, $, #, @, !, \, /, :, *, ?, ", <, >, |, ;, ' etc are contained in names of vSphere entities such as virtual machine name, cluster name, and datastore/folder/file name. However, '-' and '.' is apparently supported. KB
Here are the test results:
To be inline I did a check on Microsoft Active Directory DNS, 64 characters are the maximum allowed for a DNS name and 255 characters for a FQDN as stated here.