This was originally posted on APC forums on 6/1/2015
Yes, AC voltages are in RMS.
As for discovering electrical problems, to set your expectations: the UPS isn't a power line diagnostic tool so capabilities are limited. The log will show if the voltage is high or low or the frequency out of range over an extended period of time. Electrical issues over a short timespan may not show up in the data log*, but may cause the UPS to transfer to battery which will show up in the event log. Issues with grounding, missing neutral, neutral and hot swapped, etc may show up as "site wiring fault".
* You'd think they'd show up in Vmin and Vmax but unfortunately brief events do not necessarily show up here.