The federal statute concerning the stimulus checks exempts them from being counted as income by any federally funded program like Medicaid or SSI. Further, the checks are not counted as resources in the month of receipt or the following two months.The Center for Medicare and Medicaid Services (CMS) issued a notice on this issue which can be found here: Treatment of Economic Stimulus Tax Rebates

The CMS notice provides, in part, as follows:

The economic stimulus legislation … provides that credits or refunds issued under the bill are not to be counted as income or resources in the month of receipt, and for the following two months, for purposes of determining eligibility for or the amount of benefits under any federal program, or under any state or local program financed in whole or in part with federal funds. … [Further,] rebates given away during the three-month period in which they are not countable as income or resources would not be subject to a transfer penalty. However, if given away after the three-month exempt period expires, the rebates would be subject to penalty.