When you create a vault can you move the vault to say an external HD? if so can you remove the pictures from your aperture library and say still update a web gallery?
A vault is an archived copy of the Aperture Library and it really should be created on an external drive. There is little point of keeping your backup in the same drive as the library. So external drive is the normal place for it. Some people will have multiple vaults and rotate them in to be sync's and then rotating the drive out to some far away place.
No, if the image is not in the library you can't do anything with it
A vault is not a place to store off-line images. For that it is best to export a project. Projects can by moved off line and aperture retains the thumb nails.