You cannot hide or remove the iRadio App, however you can disable it by signing out of your Apple ID in Settings for iTunes & App Store.
1. Tap on the Settings App.
2. Tap on iTunes & App Store
3. Tap on your Apple ID.
4. Tap on Sign Out.
This will prevent music from playing in iRadio and the downloading Apps.
* If your Apple ID is greyed out for this process, you'll need to Allow Changes in Restrictions (see below).
Allow Changes in Restrictions.
1. In the Settings App tap on General.
2. Scroll down and tap on Restrictions. (Type in your passcode.)
3. Scroll down and tap on Accounts.
4. Tap on Allow Changes.
* You'll need to change it back to Don't Allow Changes after signing out of your Apple ID.