May I point out that all a RAID1 does is sync the blocks between two drives. It won’t protect against writing something dumb that would mess up the filesystem, it will just dutifully sync it.
You should be able to back up ext data from a filesystem on a RAID array, unless I’m confused about what e2image actually does. Are you trying to use it on the underlying drive devices by any chance? You have to point it at the RAID device on top of them, something like /dev/md1 rather than /dev/sda1.
This sounds like a good extra backup to have but don’t let it lull you into a false sense of security. It may help recover from a very specific kind of mistake but the recovery may be very specific as well. It’s not file backup.