Can an Arduino be used to read data from a serial port?
Yes, it can, and the wiring diagram you have drawn works perfectly for me using minicom in Ubuntu.

The majority of serial communication is bi-directional anyway - especially when using it to program a device.

There is absolutely no difference between interfacing the built-in USB->UART adaptor to an external device of your choice and interfacing it with the ATMega328P chip. Just because the ATMega328P chip is on the same board doesn't make it in any way special - it is just a UART interfaced device.

If your setup is not working you can try:


Physically remove the ATMega328P chip to see if that is interfering even when held in reset
Check for software that may be interfering with your communication, such as the notorious ModemManager.