Here are some guidelines as to how much AAs can contribute to adventures.
Low - Absolutely nothing; they can offer advice and administrate, but not add anything to adventures.
Medium - These are a cut above average, but still can perform great miracles. IF the AA has suitable skills/powers AND he rolls well on the adventure action, he might give a supportive bonus. Also, since his level is probably fairly close to that of the regent and other AAs he can join in on real adventures and actually contribute to their resolution.
High - These rare AAs are true heroic individuals (or at least VERY good at their non-heroic jobs). They can regularly solve events by adventure and usually give a supportive bonus when they are assigned such a role (but the bonus is usually bigger if they have very suitable skills for the task at hand). Also they are quite tough, and will tend to survive even dangerous adventures.
Very high - Same as high, only even more skilled. Not many domains have AAs of this level. Survival rate is very good except against the most horrible of enemies. Tuornen does in its elf general, but there are not a lot of others.
Legendary - Right...there are some legendary NPCs out there, but they are exceedingly rare. Given the low level, low magic nature of the RoE campaign these characters can start to do thinks that are quite beyond characters of other levels.
Near-epic - Even more right...the number of 16+ level characters is so small as to be non-existent.
Epic - Hahaha...try hiring the Gorogon!