To be fair to the broker, to the best of my knowledge UB only changed their rule about mandated salary accounts in August 2016. Prior to that, all you needed was an account.
Your post serves a good notice particularly to anyone who drew down prior to the rule change, and then changed to the newer loyalty rates, as they might not have seen the rule change.
Their systems are shocking, so it's probably just a periodic check they run. I suspect not having the DD coming from a UB account is probably a red flag if there's any element of manual review required.