I don't think HR or verifying agencies CAN dig into your social media. I think it's just credit scores and criminal convictions.
But, even if that's not true, which is very possible, I guarantee that your potential boss and any co-workers involved in the hiring process will Google you. That usually brings up court cases or newspaper stories (if there are any), a Facebook, or LinkedIn. If you were dumb enough to post your Reddit name on Facebook... good luck on your job search.