The link doesn't work for me so here 2 of the pictures from Westvleteren about the open fermentation. (low quality)
I think there is always a risk when using open fermentation, but it is the old way so I bet it can really change the taste of the final product.
They must work very clean. I wonder if they ever had infections.
What does the air contain in a closed room where loads of cleaning products are used? I mean what is still there that has a positive effect on the fermentation?