Yes, I installed a plumbed Miele CSO XXL under the counter in my previous house. It was on the island and I was able to use the water/drain from the prep sink in the cabinet next to the CSO. Look at the Miele CSO installation manual. They give the specs on how to do the under counter installation.

I had no issues with the CSO. It isn't the ideal position as you do have to bend down a bit, but perfectly functional. It was my 3rd oven as I also had a 48" range with 2 ovens. I used the Miele CSO 90% of the time and only used the range ovens when we had large groups over.

Don't have a great photo from that angle, but you can see the Miele CSO on the right side, under the corner of the island.