How to monitor Database usage
This sounds like a job for SP_BLITZ,SP_WHOISACTIVE etc. By Brent Ozar &amp; Team.

https://www.brentozar.com/first-aid/

Edit, I'm not advertising for them (it's a free resource anyway).  This is exactly what I've used for this exact scenario.  3rd party apps and their rogue developers killing the DB.

You might also want to limit them to using views/procedures that you write/have control of in order to get their data.

Edit2: And I just realized this is an old question that got bumped somehow.
My answer stands.