That is how the argument came up because terrain and craters dont take damage so I thought that it had to be refering to buildings. I reread it a couple times after I posted the original message and it seems a clearer then I originally though.
"Crushing: (Permanent) When you execute a movement, the vehicle can inflict impact damage to a token, component, or element that it crosses on its path regardless of the token armor. This does not stop movement. The force of impact is written inside the symbol."
There is a 4 written in the symbol. There is no "+" next to the four.
We ended up agreeing the the spider could walk over the building and would do 4 damage to the building when he did with any die check.
Now considering that the Zirl's objective to to destory a building that can take 6 point of damage and the Zirl get more point to build their army this seemes horribly out of balance. It was not. The Legion start very well covered with many windowed locations where they can fire freely with the Zirl target at a -2.
I ended up using jumpers to infiltrate bases and bunkers. Hid the command center with my deleters. Hide the Spider behind some cover and waited till the jumpers cleared out some of the Legion's snipers. By that time the deleters had done 4 of the 6 needed damage to the building and the only reason I finished off the building with the spider was because it could do the 2 damage in 1 order round while the deleters would have taken two. This could have been disasterous because my opponent had damged the A1 and E locations of the spider leaving him a 50% chance to destroy if he were to hit. That would have completed his objective.