Yes, that is exactly right.  The 'isi devices -a discover' command will list the Serial number, Product, Version, and Status of each node that is available to be added.  When adding a node, the 'isi devices -a add -d ' command will simply return with the following line:  'add' action initiated.  The additional node will be added to the cluster in roughly 60 seconds and can be seen in the WebUI under Cluster Overview and the CLI with the command 'isi status -q'.
# isi devices -a discover # isi devices -a add -d 
How to add a node(s) from the cluster end via CLI?