As far as I know, no one who are responsible about reviewing and approval process of App Store has never answered here in the dev forums.
So, you may need to consider all the description in the App Store Review Guidelines.
About gambling apps, it has a strict description about legality:
5.3 Gaming, Gambling, and Lotteries
(There are other descriptions about gambling or real money, you may need to check all of them by yourself.)
Gaming, gambling, and lotteries can be tricky to manage and tend to be one of the most regulated offerings on the App Store. Only include this functionality if you’ve fully vetted your legal obligations everywhere you make your app available and are prepared for extra time during the review process. Some things to keep in mind:
5.3.1 Sweepstakes and contests must be sponsored by the developer of the app.
5.3.2 Official rules for sweepstakes, contests, and raffles must be presented in the app and make clear that Apple is not a sponsor or involved in the activity in any manner.
5.3.3 Apps may not use in-app purchase to purchase credit or currency for use in conjunction with real money gaming of any kind, and may not enable people to purchase lottery or raffle tickets or initiate fund transfers in the app.
5.3.4 Apps that offer real money gaming (e.g. sports betting, poker, casino games, horse racing) or lotteries must have necessary licensing and permissions in the locations where the app is used, must be geo-restricted to those locations, and must be free on the App Store. Illegal gambling aids, including card counters, are not permitted on the App Store.Lottery apps must have consideration, chance, and a prize.
If you think you can fulfill all the requirements shown in the documentations or announcements of Apple's, there might be a chance your app would be approved for App Store.
