I guess it looks like it in the picture. Never noticed until you said something. The shelves are held with 8 screws each so I don't think it's going anywhere. I guess it would be wise to find out the weight limitations of the rack.
Most network racks can hold 1000-1500 lbs, so you're OK there. I guess the real holding capability comes down to the individual shelves. In addition, you need to factor in weakening due to heat.
I don't think you can get any more efficient in your space usage than the setup you have here. When not being used, your rack fits nicely in less than a 24" by 24" square.
There's a lot of potential for different ways you could configure a network rack to be used as a brew tree. You could even turn the rack sideways and have shelves off-set with one kettle on the left and one on the right. I think with any off-set weighting you'd want to bolt the base though. I think there's a lot of flexibility in this and more people should look at these. They're cheap too!