Since it was March when i was there i cant say for definite.... but since no one else replied thought it may be useful.... There are excellent roads in alot of Laos, american money i beleive, and would be surprised if they became impassable but i would imagine Cambodia a very different scenario. The roads directly around Pnom Penn are ok but outside of this they tend to be rough dusty (in dry weather!!) tracks... i think you would have alot of problems when they get flooded out.... the journey to and from Angkor Watt for instance would be hellish.... i then went north directly into Laos and couldnt imagine this being at all posible in bad weather with a loaded bike....
Thats my imput on it... anyone else know better??
Anyway, best of luck.
Some day so soon....