I understand your goal and the idea isn't bad, it's just not possible. Now, what IS possible, if you really want to do this and are set up as I imagine you are from the description (that is, assuming that this is a data-only array and not the OS... so we assume that the OS is always still intact...)
Have a WARM spare (no such thing as a HOT spare with RAID 0, it just is nonsensical, it's a meaningless term to use in that case.) This will sit idly by. Have a monitoring script that looks for an array failure. Have the script talk to the Smart Array utility and disengage the dead drive. Have the script talk to the utility and add in the WARM spare to a new array group. Have the script built a new RAID 0 array. Have the script unmount the old array and remove any legacy bits of it. Detect the new array. LVM the new array. Format the new array. Mount the new array. Signal to the node that it is ready to proceed.So I think that this does what you want, but it is not a HOT spare and it is not the RAID controller doing the work, it is your own script. So your end result can be done, just not using the exact tool and location of tool that you were imagining. But having a spare on board and rebuilding the system is possible.
But most likely there will be a better way to skin this cat. But I can see a potential use case for this.
