As far as I know only camera roll pictures can be deleted off an iPhone & camera roll photos are included in the back-ups...
http://support.apple.com/kb/ht1766
The relevant entry from the support document, as it does list camera roll pictures and videos in what is backed-up.
iTunes will back up the following information:
Address Book and Address Book favorites.
App Store Application data (except the Application itself, its tmp and Caches folder).
Application settings, preferences, and data.
Autofill for webpages.
CalDAV and subscribed calendar accounts.
Calendar accounts.
Calendar events.
Call history.
Camera Roll (Photos, screenshots, images saved, and videos taken. Videos greater than 2 GB are backed up with iOS 4.0 and later.)
Note: For devices without a camera, Camera Roll is called Saved Photos.
In-app purchases.
Keychain (this includes email account passwords, Wi-Fi passwords, and passwords you enter into websites and some other applications. If you encrypt the backup with iOS 4 and later, the keychain information is transferred to the new device. With an unencrypted backup, the keychain can only be restored to the same iPhone or iPod touch. If you are restoring to a new device with an unencrypted backup, you will need to enter these passwords again.)
List of External Sync Sources (Mobile Me, Exchange ActiveSync).
Location service preferences for apps and websites you have allowed to use your location.
Mail accounts.
Managed Configurations/Profiles. When restoring a backup to a different device, all settings related to the configuration profiles will not be restored (accounts, restrictions, or anything else that can be specified through a configuration profile). Note that accounts and settings that are not associated with a configuration profile will still be restored.
Map bookmarks, recent searches, and the current location displayed in Maps.
Microsoft Exchange account configurations.
Network settings (saved wifi spots, VPN settings, network preferences).
Nike + iPod saved workouts and settings.
Notes.
Offline web application cache/database.
Paired Bluetooth devices (which can only be used if restored to the same phone that did the backup).
Safari bookmarks, cookies, history, offline data, and currently open pages.
Saved suggestion corrections (these are saved automatically as you reject suggested corrections).
SMS and MMS (pictures and video) messages.
Trusted hosts that have certificates that cannot be verified.
Voice memos.
Voicemail token (This is not the Voicemail password, but is used for validation when connecting. This is only restored to a phone with the same phone number on the SIM card).
Wallpapers.
Web clips.
YouTube bookmarks and history.
