VM/Template name was suggested by Greg to stay limited to 40 chars on CFME side to avoid RHV version specific logic, but in the commit [1] VM/template Name was also updated to 255 chars limit.
As Ilanit specifies in the first comment, RHV limits VM/template name to 64 chars, so attempt to provision VM with name longer than 64 chars fails.
[1] https://github.com/ManageIQ/manageiq/commit/0ae390bc3049e2121a125b8b48dc49eb659a514f
Radim - As discussed here https://github.com/ManageIQ/manageiq/pull/16736#issuecomment-355107499 I suggested that we use the larger value now as that will be the supported value going forward.
If a user has a need to enforce the 64 character limit they can do that by modifying the dialog to meet their needs. This option has been available for a long time in the dialogs.