The only things they could get from scanning the oval would be how banked it is and how concave the surface is, but you wouldn't need to scan the surface to get those measurements. As far as the surface goes, it won't have weeds in it, as it was recently sealed with a protective layer to prevent further degradation, as well as the line was re-pained, the rusted guardrail was replaced, and the bushes and weeds were cut back.
However, the underlying structure of the banking is made of large concrete sections, that have continually moved over time. This was what led to the course becoming too bumpy to race on, making high speeds increasingly dangerous on the banking year after year. I can only imagine it would be atrocious now, as it was deemed too bumpy in the 1960's.
The only measurements they'd need would be the height at the highest point relative to ground height, how low the lowest point of the banking is relative to the ground (the lowest part of the banking is lower than the ground), the width of the road at various points, the degrees of banking at various points, and the level of concavity at various points. They don't need to scan it to get these measurements, but perhaps they had the equipment there for scanning the modern circuit, and figured they may as well scan the banking to get those measurements that way. That's the only way scanning that surface makes sense.
Edit: In any case, I'm really looking forward to it, as Monza is one of my favourite circuits, and I believe Kunos will make a very good replica of the historic version.
On another note, at the historic 1966 Monza already in AC, is it possible to drive on the curva nord est, the reverse parabolica of the Pirelli test course that was built from paving stones from the original circuit (pre-war), and was never used? I see in videos that the road is there, coming off the road course just before curva grande, and it would be very cool if we could actually drive on that course.