Either way fan service is a thing, you can love it or hate but it won't go anywhere. There's not much that can be done, and Zack did win the tournaments, He won by default in. DOA3 since Ayane didn't claim the prize money. Same with DOA4, Helena gave Zack the prize. As far as the games go, they are canon, the Zack island is a thing in the main series, Zack has a hoodie that promotes it as a trademark and the actual island is a stage, plus certain girls have the logo I think on their heel sandals, so yeah its canon.
This is DOA, the girls all have various reasons to go on the island, no matter how ridiculous or strange they are, they went, DOA is basically about sexy, buxom women fighting so going to the beach isn't a stretch. Plus the pose mode where you can take pics is only pervy if you make it so, like I said before the game developers implemented the girl's negative reactions to certain poses and positions which shows they aren't comfortable with it. You can peek and stuff yes, but there's moral repercussions to that, unless you're sick in the head you wouldn't want to upset your favorite girl and have her hate you for intruding on her privacy.
Back on topic, I wonder if two guys will be featured in this one like they sometimes do in these packs.