According to the IRS, who I called this morning, YES. People on SSI are not eligible for the rebate. A 2007 federal tax return must be filed to receive the rebate even if you usually do not file. I will try and find a reference to this information today, as I do not trust information from an informal phone call to the IRS.
Some low-income workers and recipients of Social Security,
certain veterans’ benefits and certain Railroad Retirement benefits may qualify
for economic stimulus payments this year from the federal government.
If you etrapolate the information people on SSDI who received at least $3000 in income are eligible. I called my congress critter, Peter Defazio's office and they were unclear about folks receiving SSDI, but the IRS said we were eligible. I would like to find a clear reference to this, as I am cynial, and will update this post if I find a clear reference.