Pharma firm Bayer has created a DS plug-in built on the idea that diabetic kids typically lose track of no-fun things like glucose meters, but rarely lose fun things like gaming handhelds.
No, the "Didget" isn't a kind of Vitality Sensor; it goes into the DS/DS Lite's Slot-2 and rewards players giving consistent readings with points in a game that can be used to buy items or unlock levels. It doesn't sound like the game itself has anything to do with diabetes or testing, it's just the vessel through which the Didget rewards a player's consistent monitoring.
I'm not in a household with a diabetic child, but I was in one with a recently diagnosed adult; I can testify that testing yourself can be a real bitch, and doing it consistently requires some discipline, which younger kids may not have. The Didget sounds like a helpful peripheral, although some might think buying a video game attachment rewards, rather than corrects, a kid not taking responsibility for himself. I guess it depends on the age. One thing, however, since this requires Slot-2, it's not DSi compatible.