Wow, @luz, thanks, man! Got the thing working!
To complete the thread, here's what I did:
Implemented the "INIT" command in my Omega-Arduino serial protocol. Before receiving "INIT" command, Arduino swallows up anythin that is thrown at it, and does not return anything back. Only after the "INIT" command it starts to accept other commands and return responses.
I changed the /etc/inittab file, commenting out the line that makes openwrt await a login on the console:
#::askconsole:/bin/ash --login
Edited the /etc/sysctl.conf file, adding a row at start, to prevent the kernel from writing any messages to the console:
kernel.printk = 0 4 1 7