Re: Add old drive to RAID controller but keeping the data?
The good controllers will allow you to set up a RAID array that was running once before, but you should always have backup copies of data on a RAID 0 array anyway, since without both drives, you're essentially hosed. If one of those drives died in the time between taking them out and reconnecting them for example, you'd be extra boned.
To answer your question though, I've put two drives on a RAID controller (in RAID 0) and told the controller NOT to re-initialize the array and just go with it AS IS, it worked fine. But I don't recommend the practice, especially if you have no backups of the data.