identifierForVendor for iOS6 or later. What about identifying iOS5 or earlier devices from the same app?

Question

I needed a unique ID for each device which uses an app built in Xcode 6.1 (iOS 8.1).

I have used identifierForVendor for devices with iOS 6 or later. However the app is also meant to support iOS 5 or earlier devices. So what I did is

if ([[UIDevice currentDevice]respondsToSelector:@selector(identifierForVendor)]) {
   return [UIDevice currentDevice].identifierForVendor.UUIDString;
}
else{
   return [[UIDevice currentDevice] performSelector:@selector(uniqueIdentifier)];
}

But some of the posts like this and this say that it would be rejected by Apple if uniqueIdentifier method is called.

If that is the case, then can someone please guide me how to do this?

Thanks.