I am also searching for an answer to this question. After a couple of hours of tedious research I've managed to conclude that the VT6103/VT6105 are probably supported.
A user on the mailing list here:
http://m0n0.ch/wall/list/showmsg.php?id=184/22 claims to have m0n0wall (ver 1.11) working on the VIA EPIA PD-6000E which according to the manual here:
http://www.via.com.tw/en/products/mainboards/downloads.jsp?motherboard_id=241 uses the 6103/6105 combination.
It would be really good to get complete confirmation that the current version of m0n0wall supports these chips though.
There are lots of dual-nic VIA ITX boards that look absolutely ideal for running m0n0wall.
I'll report back with any other info I come across.