I'm doing the C25K and dieting so don't have any firsthand experience to share.  I will say that if you consume as many calories as you're burning during the program then you won't see a loss.  If you consume fewere you will see a loss.  My husband took up running a couple of times a week about a year ago and has not coupled it with dieting.  He has lost weight but very slowly.  The upshot of all my rambling is it just depends.  

I graduated from C25K in November and I can absolutely positively say...it depends.

If you go by the basic calories in -vs- calories out theory then you could certainly lose weight just by adding C25K, but there are a few buts.  This is assuming you don't change your eating habits at all and that you weren't putting on weight before you started, i.e. if your calories in before were too high (putting on weight) then adding more activity may not be enough to swing your calorie surplus the other direction.  On the other hand, if your weight is rock steady with your current diet and you add more activity to your day like C25K then you should certainly see some weight come off.