When you send things using your gmail address, you still retain the IP rights to your material and property attached inside, but you also give Google a perpetual, unrestricted, non-exclusive right to that material, should it be looked at and deemed interesting.
The same thing probably applies to stuff made in this app by Apple.
If I came across that in an Apple EULA I wouldn't be surprised, but I've read several EULAs found at the site I linked to and haven't found any language that suggests what you describe.
The same thing probably applies to stuff made in this app by Apple.