There are certainly people out there with trading bots hooked up to the various exchanges. I know at least one guy who was trying something a few years ago. Because the volume is so low (~ few $M daily) I don't think there are any big players there. Also the market data and order entry protocols don't look like they would be suitable for the really high speed stuff.

That said, the market data and order entry protocols are really simple and I think most exchanges offer them for free. An automated bitcoin/dollar trading program would be a pretty easy thing to whip up. It would probably be a good introduction to automated trading for people that are interested in that sort of thing.