It'd only be fraud if the government was paying for it.
[Edit]Some hate against my comment. For those that fail to understand...
It isn't fraud if you go to a gas station that is charging $0.10 more a gallon, and fill up there. It's fraud if you pay for that gas, and its water. The insurance is still buying the same drug, they have just chosen to negotiate a price that is higher with one hospital than another. They have their own reasons for deciding that price.
Likewise it would be fraud if the government was paying for it, since they have set rates. To achieve a higher payment would require billing them for some other product.