The focal length should be fine, at an indoor trial. 400 would be GREAT, but 200 is certainly workable. My "dark building" lens is a 200mm prime. The added flexibility of the 70-200 should serve you well.

The one concern, depending on the lighting, might be that 2.8 isn't bright enough, but with white dogs, you'll have an advantage there too.

I'd love to go to an all Eskie trial.