If you back up your iPad to iCloud, the backup will include photos stored in the camera roll. The photos will not be accessibile to download or view; they will only be available to restore to your device as part of restoring the entire backup. You would not be able to access the photos contained in the backup on your MacBook when you get home. The backup counts against your iCloud storage space.
Alternatively, if you upload the photos using Photo Stream, you can upload up to 1000 photos for up to 30 days. Photo Stream photos can be accessed via iOS devices and computers signed into the same iCloud account that also have Photo Stream enabled. If your MacBook meets is running OS X 10.7.2 10.7.4 or higher, you will be able download the photos from Photo Stream. This article explains how to set this up on your Mac and other devices: http://www.apple.com/icloud/setup/mac.html. Photo Stream photos do not count against your iCloud space. Another thing to be aware of is that photos uploaded to Photo Stream are streamed back to your device to a Photo Stream album, so you will end up using additional storage space on your iPad when you do this. Here's a FAQ on Photo Stream that you may find helpful: http://support.apple.com/kb/HT4486.
Edit: Your MacBook must be running OS X 10.7.4 or higher to sync it with iCloud and enable Photo Stream.
I am STILL searching for a definitive answer to this question.
My iPad, by default, shows three albums:
Will an iCloud backup include all of these albums - or ONLY the Camera Roll?
I'm interested only with restoring all of my imported photos to my iPad if the need arises.
Here is my understanding
The documentation is pretty clear that iCloud backs up Camera roll. I believe the programming assumption is that you already have "imported photos" backed up elsewhere.
If you do not have a back-up for your imported photos then there are Apps in the App store that will allow you to transfer IPAD potos (imported photos) to another device for back-up. I beleive it imight be the Photo Transfer App.
Photos should be regularly synced to a computer (like you store photos from a digital camera) using either USB via iTunes (on a mac use iPhoto or Aperture to move them to an album) or using photo stream. If you have been doing that, then you can sync those photos back to your device.
If you haven't been saving photos except relying on iCloud to store them in a backup, then that is risky, as many users have discovered (they've lost photos, those that should have been restored from a backup but that in fact didn't appear).
I've been using my iPad as a standalone computer, with no connection to iTunes. I am concerned about backing up photos imported from a digital camera using the SD card adaptor. If only the actual Camera Roll album is being sent to iCloud, then I'll just have to make a point of moving my images over to it before backing up.
Ideally, it would be great to mount a second "backup" SD card to the iPad - and copy images to it for safe keeping.
Yes, you are correct.... there is a small wiggle room.
Your photos MIGHT still be in iCloud storage for a bit, "your phone will automatically back up your camera roll, accounts, documents, and settings when your iPhone is plugged in, locked and connected to wifi.". This statement is from your iPhone iCloud back-up screen
So if all three of these constraints are not satisfied then iCloud storage will keep your photos until these constraints are met or unless you tap 'back-up now" on your iPhone or when connected to iTunes on a computer.