Fraud is an intentional tort. If they never intend to give the rebate for all eligible people, then it is fraud if they then do not actually do it (even if you don't complain). If not enough money is allocated up front, and if they run out of money to pay all the eligible rebates they receive, then it seems to me to be fraud (although IANAL)...
Well, the question comes down to what happens if every single person actually does comply with the terms of the rebate and requests it. It seems like either some party (either the company that offered the rebate, or the company that the rebate handling was outsourced to) will be forced to cough up the extra money to cover every rebate, or they will fail to pay out the rebates.
You seem to be assuming that the latter is the guaranteed result, but I don't see that it is. I'm not privy to the details of these contracts, but I would be amazed if they don't, as a general rule, spell out who is responsible for costs that exceed the expected cost of the rebate program.