This seems like a really awkward way to replicate a drive. Usually replicating a drive is quite easy, especially if you are using the exact same type of drive.
What kind of drive is it and what do you want to do with it?
To me replicating a drive starts with the dd command, the basis is
dd if=[name of the input file,drive,whatever you want to make a copy of] of=[where you want to write the copy to]
The destination (and source for that matter) can both be nearly anything. the if could be "/dev/[your raid array]" or a file or network stream that offers the right kind of data to write to the disk. The of could be a file that holds all the data on a different network location and then on the second server(the new one) you just use the network location as input file(if) and the raid array as output file(of).
The dirty way you are talking about is just bad... it's running the risk of losing everything and I'm not even sure it's easier. Of course you could try it and if your drives are hot swapable you can just remove them and put them back in. http://www.debuntu.org/how-to-rescan...hout-rebooting
might help you out on detecting a new drive if it does not automatically is recognised by your raid hardware. If you're using software raid I would like to point you back to my first suggestion.