We are in Florida and had a similar requirement to display the status of our AVR. We had Wartsila put a display on the WOIS (it sounds very similar to what you did). After a few weeks our operators questioned whether or not the AVR status was accurate. We checked by forcing the AVR to manual using a DI on the AVR itself (send me an e-mail if you want details) and the AVR status on the WOIS was not correct. Wartsila had to go back and fix the status. I’m not sure how you tested the display on the WOIS, but this doesn’t seem like something Wartsila does very often and it would be a good idea to make sure you tested that the indication was accurate.
The PSS is built in to the Unitrol 1020; it is enabled at whatever power level you put in the settings of the AVR.