Fair concerns..

Steemit is open source: https://github.com/steemit/steemit.com , most of its data is stored on the "Steem" blockchain (also open source: https://github.com/steemit/steem), although there could be a user-account related private database behind the site itself. IMHO you would be welcomed if you have interest to do the test, since it would benefit the whole platform, however perhaps you want to contact the company (Steemit, Inc) first to get a permission or somewhat similar. There is a public email address [email protected], also you can send direct message to @ned and/or @sneak on https://steemit.chat/ , and feel free to contact me by replying to this comment if above methods don't work for you (I'm not always on steemit.chat but occasionally check replies on this website).