You can backup to iCloud but read this for more information and make sure that you read the relevant links in the article as well. Not all of your iPad content may be backed up to iCloud so you know what is and what isn't backed up.
How to backup
Have you tried rebooting your iPad?
Reboot the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the buttons.
iCloud: Backup and restore overview
Check iCloud storage & backup space on iPad
iCloud: Troubleshooting creating backups
"So what exactly does iCloud Backup take care of? According to Apple, your device’s settings; app data; the Home screen and how your apps are organized; photos and videos in the Camera Roll; iMessage, SMS, and MMS messages; and ringtones will all be uploaded."
i think the photos must be in the "photo stream" section. but how to make that if the photos were taken before i activated the streaming-icloud!!!??
in the other hand, icloud.com does not show any Photo icon!!
ok, just to let you all know !!
i decided to completly restore my ipad, and erase all content etc(i just did the normal icloud backup before)
after restore, it was obviously empty(like new). i then pull back the backup(from icloud to my just restored ipad)
everything was there!! even the photos, that weren't in the photo stream!!!
so just sharing my experience!! thanks everyone!!