Pre-select a role on user register form and hide from display?
well..after staring at this question and trying a bunch of things on my own I think I stumbled upon the answer. Using HOOK_user_presave did the trick! This helped immensely: https://drupal.stackexchange.com/a/79065/28353 

function mandatory_role_user_presave(&amp;$edit, $account, $category) {
global $user;
if(in_array('venue admin', $user-&gt;roles)) {
  if($account -&gt;is_new) {
    $roles = user_roles(TRUE);
    $rid = array_search('customer', $roles);
    if($rid != FALSE) {
      $edit['roles'][$rid] = 1;
        }
      }
    }
  }