Based on the photo of concrete pump truck action at the No. 4 reactor below, the currently used vehicle seems only enough to reach the edge of the buildings, so I guess it will help to better reach the parts of the top floor further away from accessible sides. (I'm not sure though whether the arm can be telescoped out further, but none of the photos I shaw showed it reaching further.)

I heard they are going to use dust absorbing powders to clean the air

No, resins to prevent dust on the ground being picked up by wind.

Fukushima plant groundwater likely contaminated despite data error | Kyodo News

In an effort to prevent radioactive dust from being dispersed by wind and rain from the plant, TEPCO will begin a test spraying of a water-soluble resin, which has coating effects, later in the day.

As a result of hydrogen explosions, masses of debris have been strewn around the site, which was ravaged by the March 11 earthquake and tsunami. A total of 60,000 liters of resin will be sprayed over a period of two weeks.