Cellulite only describes the "appearance". It is named for the dimply texture on the skin resulting from the way the adipose (fat) cells are stored. Alot of times it is seen on the buttock, and thighs of women because of the weaker network of collagen (the fat pokes through the weak spots, like dough would in a straw basket).
Those cellulite creams only work to thicken the skin so that the lumps are less apparent. It is like throwing a thicker blanket over stones...you will not see as many lumps.
If it is a simple layer of fat on your tummy that you are talking about, then it is pobably not cellulite, I am guessing your belly is quite smooth. I have never seen anybody with cellulite on the tummy area before, so I would think it highly unlikely on you.