Is the calorie counter in The Biggest Loser Ultimate Workout accurate?

No the calorie counter is not accurate. It as horrible in the older Wii version. A lot of factors go into calorie burning calculating which are typically your weight and intensity. I have seen that achievement as well but didn't look for a status tracker or anything like that. You just have to keep playing and you will eventually get it. Two ways I have experienced shedding 10+ calories a minute are on an elliptical machine and jogging above 4mph. If you want a more accurate reading get yourself a heart rate monitor and see how many calories that says you burn. Good luck on your achievement.