Is it possible to move photos from your iPad to the iCloud, keep them there but delete them off the iPad?
If you have Photo Stream enabled, they will stay there for 30 days.
This gives you enough time to download them to your computer.
See this -> iCloud: Photo Stream
and this -> iCloud: Photo Stream FAQ
Or you can sync them directly to your computer
I have this question too. I seem to have plenty of space in my cloud, but my pad is maxed out. I want to delete photos and videos from my pad, but keep them in the cloud, much like a regular computer and a camera. How do I keep the videos and photos that are important to me but free up space on my pad?
The only way to keep those pictures permanently is to import them into a Photo app on your computer. iCloud backups are overwritten so once you back up your iPad without the pictures, that will eventually overwrite the backup that has the pictures. iCloud is not a place to premanently store anything. It is a backup of your current state so that you can restore to that in the case of a hardware issue.
Import the pics to your computer, and the back those files up to an external disk or flash drive. If you don't do this, you are risking permanent loss of those important photos and videos