How can I hook into an entityform submission?
If I understand your question right, you should use the following hook to capture a submission:

hook_entityform_insert($entityform)


As described in the comments at the top of entityform.api.php:

* Entityform and Entityform type are standard entities using the Entity API module.
* The standard Entity hooks are availabe for them.
* Including
*  ...
*  hook_entityform_insert


Hope this helps

Addition:

here is the sample code I used:

function mymodule_entityform_insert($entityform){
  dsm($entityform);
}


and it did get triggered as soon as I submitted an EntityForm.