By the way that character of mine also has a nasty sneak attack as well

(also soloed the Proving grounds in Z EfU mod)
The UAI ability is "usually" linked to the cost of the item. The higher the cost the eaiser you can use it.
The Grimoire is the best NWN manual I've found. There is a table on page 98 that shows the amount you need to invest in the skill.
Basically you should be able to use all scrolls and most items.