The NEC has been migrating away from using the grounded conductor (usually a neutral) as an equipment ground for quite some time. The general rule is once you pass the service disconnect, equipment grounds and grounded conductors are to be separated an the grounded conductor should not come into contact with a grounded enclosure.

The CH catalog for their spa disconnect shows two factory installed bus bars.

Few things are harder to put up with than the annoyance of a good example.