We can rediect serial console to other device using socat.
The testbed is:
In this case, /dev/ttyUSB0 is redirected by socat,
in Dom0
$ socat TCP4-LISTEN:54321,reuseaddr /dev/ttyUSB0,b115200,nonblock,raw,echo=0
in DomU
$ socat PTY,link=/dev/vmodem0,b115200,raw,echo=0,waitslave TCP4:192.168.1.254:54321
in DomU, we can access Arndale's UART via /dev/vmodem0, using minicom