Is it possible to replace a 5/i controller without losing the data on the array? Can I import this as a foreign configuration? Any "gotchas" or tips to make this smoother?
I can't give you any 100%, because it may be different for any number of reasons, but I have done this before and got my drives back. I just imported the foreign configuration and Voila! my RAID was back (RAID 1 - 2 disks). However, if the system is still under maintenance I would just try and have Dell walk you through it.
RAID information should be stored on the disks themselves, and not on the actual controller (that's why if you move disks around, the server can see that they have been moved). So you should be able to replace the controller with no issue whatsoever (but a backup is always a good thing in case something goes wrong). As mentioned above, having dell on the hook is in your best interest should something go wonky... processes dealing with storage can always be kind of hair raising.