Cable wise connection it is potentially possible. I have tried to connect my external SmartDisk hard drive (USB) to a serial port:
SmartDisk -> USB male -> mouse adaptor [USB female -> PS/2 male] -> serial adaptor [PS/2 female -> Serial female] -> male Serial in the computer.
Connections are not signals. Hardware is not drivers. The setup you describe will not work. For one thing a USB-to-PS/2 mouse adapter only works because a USB mouse emulates a PS/2 mouse in software, making an adapter very simple, only a small subset of the full specification. Also, a mouse or joystick uses slow USB, not even the full USB 1.1 bandwidth. Last but not least, an RS-232 serial port cannot emulate a USB port in software.