Same behaviour for hook host/managed/destroy.

The API shows the parameters in .parameters and .all_parameters keys:

$ curl -kns https://katello-01.net/api/v2/hosts/host-03.net | jq '{parameters, all_parameters}'
{
  "parameters": [
    {
      "priority": 70,
      "created_at": "2018-08-30 13:53:29 UTC",
      "updated_at": "2018-08-30 13:53:29 UTC",
      "id": 460,
      "name": "manage-volumes",
      "value": "true" 
    }
  ],
  "all_parameters": [
    {
      "priority": 70,
      "created_at": "2018-08-30 13:53:29 UTC",
      "updated_at": "2018-08-30 13:53:29 UTC",
      "id": 460,
      "name": "manage-volumes",
      "value": "true" 
    },
    {
      "priority": 60,
      "created_at": "2018-08-22 12:32:01 UTC",
      "updated_at": "2018-08-22 23:33:30 UTC",
      "id": 156,
      "name": "kt_activation_keys",
      "value": "upstream" 
    },
...

But the json file used in hooks does not:

$ jq '.host|{parameters, all_parameters}' ~foreman/tmp/foreman_hooks-destroy.zRfOLSZXzL
{
  "parameters": [],
  "all_parameters": [
    {
      "priority": 60,
      "created_at": "2018-08-22 12:32:01 UTC",
      "updated_at": "2018-08-22 23:33:30 UTC",
      "id": 156,
      "name": "kt_activation_keys",
      "value": "upstream" 
    },
...

I am afraid that post queue won't show any data after commit. Well that was just a guess, go and try it I created a patch for you:

https://github.com/theforeman/foreman_hooks/pull/58