Things will certainly get more difficult for these "middle men", but not by all that much. There is no need for them to replicate the retina/fingerprint scans or do anything hi-tech/expensive like that. The poor will still need to exchange the money paid into their accounts for actual goods and supplies like food and clean water. Simply giving the money directly to the poor will not affect the scarcity of these resources.

What will happen is that the poor will simply withdraw the entire sum the day it has been paid in to their accounts, and give it to these "middle men". All that changes is the direction. Instead of the welfare money flowing down from the government to the individual programs to the "middle men", it will be flowing up from the poor through the individual traders to these same "middle men".