Just be sure not to violate any of Apple's trademarks and copyright as you do so.
If Your Application includes or will include any other content, You must either own all such content or have permission from the content owner to use it in Your Application.
was once rejected because our help screen showed an image of the icon for the Settings app. The App Review Team complained that we weren't allowed to use that. I guess we have permission to use things like standard buttons (info, compose, action, etc.) but we don't have permission to use icons to reference other built-in apps.