in sage mode he can see through the samehada absorbing chakra once he finds out kisame is dusted
and gai almost killed kisame even though he had hachibi chakra
Tough match up.
Jiraiya requires a lot of time to go sage mode. If he does, Samehada will be useless. And all chakra-absorbing techs of Kisame will be useless. Sip one ounce of that toad chakra and he will turn to a toad. And that is IF.