I googled " Lego cnc nxt gcode" and got this http://us.mindstorms.lego.com/en-us/...5-420b6c2fe8a5
Seems that so long as you can output gcode, which sketchup can do with plugins. You should be able to accomplish this.
I'm not familiar with the nxt system but i think google is going to get you answers a lot faster. Cool project post some pics when you get it going.