Well pubmed studies say no, but everyone who has tried it are saying yes, I remember atleast 1 pubmed study using 1000 calories per day, and the HCG diet is 500 calories per day.
There is a study supporting it, and this is it: Invalid Link Removed
One pubmed study concluded there was a "Hawthorne effect" only in the 1st 4 weeks of using HCG, which I think theres no reason why it wouldnt be true. naturally if you are on a performance enchancer your going to have more energy and therefore burn more calories.