Question about the specifics of Yakumo's ability.

I'm currently trying to use Yakumo to get specific passives on legendary pals. My main question is this: does Yakumo's ability only affect the passives when a pal is spawned, or when it is caught? For instance, if I don't have Yakumo out when the legendary pal spawns, but take him out when I try to catch it, will it have the Yakumo passives if I catch it (assuming the 15-30% chance goes through), or does Yakumo not affect it because it wasn't out when the pal first spawned in?