Would not be considered income. Why? If my brother paid me, the $$$ would be tax free (paying me under the table).
Work income is taxable.

Besides, as of 2010 the maximum amount of income I can get without SSDI cutting me off is $1000/monthly. I don't think my brother would have paid me that just for going to the bank a few times a month.
2010 SSI amount - $720/monthly

According to the SSD website;
"You may have unlimited earnings during a trial work period of up to nine months (not necessarily in a row) and still receive full benefits."
http://ssa.gov/pubs/10003.html