If the Island that Sanji and Co. have landed recently is really Zou (Which I doubt) then with the help of Law's Vivre Card Luffy and Co. can easily meet with the rest of SH crew. But in case Sanji and Co. have taken a detour on their way to Zou (following the zoan girl/in order to save 'them') Then Sanji and Co. have to find their way to Zou (using their vivre card) and meet with Luffy's team.
Well majority of the clues point towards Zou. (including the terrain, Kaido's men waiting for a certain Samurai , and the people who are in trouble aka them[could be rest of Heart Pirates]). But some clues like, chopper mentioning "we did well to land here...we can still save them " and Ceasar's strong protest against landing on the island, points more towards a detour that they had to take.(becoz of moral obligations). And the island they have landed is merely a bait provided by Kaido.