He would be a good hypetool for Luffy.
But if that would be the case, then the chance for Sanji vs Kizaru will drop to 0

(in case he is defeated, knocked out).
Maybe some skirmish and that's all.
P.S: Why would he ally with SHs? Against who they will fight? This option makes no sense. At most he might turn a blind eye to the situation and not engaging (assuming he has some relevant relationship with Sentomaru).