Darlington Transistor functionality
There needs to be a tad bit of context for this circuit to make sense. The ULN200X series of chips are designed to drive relays and other inductive loads. VCC isn't really VCC like you think of it. That diode to "VCC" serves as a flyback diode to simplify relay connections. most datasheets refer to it as "common" since it can be very much different from VCC on your board.

This datasheet has a better idea on how that works, look at page 12 and 17.