The latter is actually forbidden per the App Store guidelines:
4.5.3 Do not use Apple Services to spam, phish, or send unsolicited messages to customers, including Game Center, Push Notifications, etc. Do not attempt to reverse lookup, trace, relate, associate, mine, harvest, or otherwise exploit Player IDs, aliases, or other information obtained through Game Center, or you will be removed from the Developer Program.
4.5.4 Push Notifications must not be required for the app to function, and should not be used for advertising, promotions, or direct marketing purposes or to send sensitive personal or confidential information.
4.5.3 Do not use Apple Services to spam, phish, or send unsolicited messages to customers, including Game Center, Push Notifications, etc. Do not attempt to reverse lookup, trace, relate, associate, mine, harvest, or otherwise exploit Player IDs, aliases, or other information obtained through Game Center, or you will be removed from the Developer Program.
4.5.4 Push Notifications must not be required for the app to function, and should not be used for advertising, promotions, or direct marketing purposes or to send sensitive personal or confidential information.