How can I force HP Smart Array RAID controller to re-recognize drives?

The removed drives still have the RAID metadata on them. When you went to step #3 in the first drive replacement process; Boot up the server and acknowledge errors about failed drives, did you DELETE the removed array/logical drive or just mark it as failed? That's probably the source of the problem here.

When you brought up the system with your old drives, you should have again deleted the new data logical drive either in the BIOS raid utility or with the Smartstart/DL180 Setup Array Configuration utility and let the controller detect the array/logical drive.

Try this. Boot up with the new drives removed. Go into the BIOS or DL180 setup disk Array Config and delete the RAID 1+0 array. Then boot with your old drives and see if they're detected. Get the data you need. Remove the old drives. Delete the array. Insert your new drives. Let the controller discover the new array. Restore your data...

Keep this HP Smart Array controller users guide handy. http://h20564.www2.hpe.com/hpsc/doc/public/display?docId=c01608507