I found out some more information about William G. Flood, the father of William H. Flood who claimed to have climbed up to the box at Ford's Theatre.
William G. Flood did know Lincoln, they were members of the Illinois General Assembly together, though Flood was a Democrat and political ally of Stephen Douglas. When Lincoln became President Flood asked for a job in the Administration as an Army Paymaster despite being a Democrat. Lincoln obliged and requested War Secretary Cameron try to find a job for Flood: