I'd be surprised if you can render TG files with backburner, as far as I know it is primarily or even exclusively for use with Autodesk products.
With Terragen 2 you have the option to set up 3 (Terragen 2) or 5 (Terragen 2 with Animation) render nodes.
I would imagine that if your render farm is extensive, then you would need to talk to the nice chaps Planetside about licencing further nodes.
Hope this helps
Chris