If it really is just plain EXT3 and RAID1 then yes, you can just take either drive and insert it into any Linux box and access it.

Don't forget that RAID1 does not equal two discs. You can have as many discs as you want in you RAID1 array, adding more hardware redundancy.

And yes, once RAID5/6 are in play you can't take single discs out and take your data elsewhere. I a RAID5 array with N discs, you need N-1 discs from the array to recover your data.

However if you are simply after redundancy they you might be just as well off with a regular rsync job that synced between two Linux based single drive NASes.