Here is a relevant paragraph from Comprehensive Rules, in case you still have doubts:
"The source of an effect is the card on which that effect is printed. Even though a card like an event may require a minion to exert to pay its cost, the source of that effect is the event card and not the minion."
The fact that exertions or anything else are needed from a character, does not change the source of the effect, hence you should be able to use attached cards or anything outside of the very card that cannot be used.