I can't believe yall are actually taking this bait
Luffy dodging the question doesn't mean he doesn't want her to join. Besides, at this point, she's already gained his trust and they were happy to see each other again when they met up vs Kaido.
Yamato is still determined to leave with him and there's nothing to suggest he'd say no when she inevitably asks to join after the war. Luffy's only criteria for asking/accepting people is if he knows they're a good person and Yamato already proved that to him numerous times.