Validation radio custom fields on civicrm_validateForm hook does not work
Make the field required all the time. Add another choice to the radio called "Not Required". In your validate hook check if the contact subtype is AA and if they chose Not Required set the $errors variable on your radio field to show your error. Since you made it a required field it will be in the fields array.

For inline edit the formName is CRM_Contact_Form_Inline_CustomData and you will need to look up the contact subtype using the api, e.g. civicrm_api3('Contact', 'get'...). Use the contact id from $fields['cid']. (Go to /civicrm/api in your browser - it's very handy for getting the api syntax correct.)

Also note your custom field in edit mode will have a different name. It won't be custom_70-1 it will be custom_70-3838 or something like that, so you'll need to either look it up from $form first (e.g. in the groupTree element) or do something like loop through the $fields keys and compare substr($key, 0, 9) == 'custom_70'.