Yup, it works just like death row. Guards pick up trays of food from the assigned canteen, deliver them directly to inmates in their cells at meal times, then collect them afterwards and take them to the kitchen for cleaning - the trays, I mean, not the prisoners! 
Of course that's quite labour-intensive if you have a lot of supermaxers. The alternative is to have a self-contained supermax wing where all the prisoners can move freely between various facilities within the block. That's better for satisfying more of their needs since you can have a yard and even a library in addition to the canteen. However that requires more space and if it's adjacent to "shared" rooms you'd probably need to add an entrance lobby coded as staff-only to stop the residents from wandering off.
