From https://github.com/theforeman/foreman/issues/1382

I quickly hacked app/views/compute_resources_vms/form/vmware/_volume.html.erb so the last lines are:

  <%= checkbox_f f, :thin, {
             :label => _("Thin provision"),
             :class => 'disable-unsupported'},
             "true",
             "false" %>
  <%= checkbox_f f, :eager_zero, {
             :label => "Eager zero",
             :class => 'disable-unsupported',
             :help_inline => remove_child_link("X", f, { :method => :'_delete', :title => _('remove volume'), :class => 'label label-danger disable-unsupported' })},
             "true",
             "false" %>
</div>

Hacked because I didn't bother with the label localization.
It doesn't work out of the box yet because of a bug in fog (https://github.com/fog/fog/issues/2857) but at least with both fixes my SAN admin is happy now :)

Sorry for not supplying a PR. Hope it's trivial enough for someone to do (properly).