Not necessarily.. if he can bang out 3 sets of 7-8 after the main lifts on SS, he can probably bang out 10 clean ones fresh. More importantly though, even 5 reps everytime you see the chinup bar is going to add up to be a LOT. The Wendler suggestion he's referring to means 50 chinups per workout.. which is fairly hard if your top set is 8.
SR, doing a shitload of chinups throughout the day is similar enough to GTG. you're way stronger than me so it's probably best to heed your advice, but my chinups went up steadily without taking them to failure and leaving a rep in the tank. done to failure you gain like 2 reps on your top set, but lose more on subsequent ones