— , If he wants a currency, with real money purchases and such, He'll have to implement the whole package, with SSL, and a webserver, otherwise, his currency won't have a value client-wise as anybody who doesn't want to pay for it just has to download "L33tHakz.apk" and can bypass any IAPs
If his game even gets remotely popular & charges money for features, there'll be hackers, but if it's clientwise level unlocking or nothing related to IRL currency, I wouldn't worry at all.