Jiraiya probably wouldn't even need frog song, based off feats. He's superior in CQC/taijutsu feats, ninjutsu feats, has multiple summons to work with, starts with SM, has Fukasaku and Shima to help evaluate Tobirama...
You could argue intel favors Jiraiya too. Tobirama doesn't have the first clue who Jiraiya is and might not even know what a Toad Sage is(although, given Hashi's SM, maybe he has some intel on sages..). Jiraiya however is going to be aware of his S/T ninjutsu(Given his student, Minato, used Tobirama's S/T jutsu) and his suiton hype.