I think there are no such template fetch functions at the moment, but it would be a nice enhancement. Can you post an enhancement request in the bug tracker?
Hi Folks, as i had to answer the same question before and solved it with some SQL query, i posted this suggestion http://ez.no/bugs/view/8906 in order to adress the common "reporting" tasks.
So, Mark, i guess, your question can be answered with SQL queries. If you have access to your DB with some GUI (phpMyAdmin, sqlPlus), i can look up the query i had.
Please note, that your question "which users have a subtree notification on a particular node" aint that easy, because the notifications are stored for the top node of that tree. Do you want to see the users that have notifications for EXACTLY this node or notifications on any subtree, that includes the particular node?