Does ATS Media function like other media hosting sites (like image shack), so can I place media in my account here for use on other sites without ever
using them in any posts/topics here?
Well once you have it up on MATS its basically a post of sorts. When you post a video or something. You will be sent to the videos page afterwards.
Then look on the right side near the bottom of the page, you will find the info for embedding on other sites aswell as ATS.