I wish I could tell how far off the calorie counter is on the machine.

A good way to give it a general check is to weigh yourself at the beginning of a week, chart your calories in for the week, chart your calories out for the week, and then weigh yourself at the end of the week. See if the numbers match your expectations. Yes, this is a pain, which is why simplified systems like WW's points/high-med-low exercise plans are easier if you plan to check this over the long term, but.

Personally, if I were trying to lose weight, I wouldn't credit myself with more than 400-500 calories for an hour of DDR. It's better to err on the safe side.