In #2451397: Entity denormalization fails to retrieve bundleDrupal\serialization\Normalizer\EntityNormalizer::denormalize() has to add _restSubmittedFields to the entity object so that Drupal\rest\Plugin\rest\resource\EntityResource::post() can work. This means that all entity normalizers would need to do this and serializers should be unaware of the Rest module.
In an ideal world the HAL module would not be dependent on Rest since it provides a serialization format that is consumed by the serialization module.