I wrote an Auction House bot and ran it for most of a year without any interference from Blizzard. It was a simple poll/buy/sell script against a price database that I maintained.
When Blizzard launched the web interface to the auction house, they also exposed a bunch of JSON accepting/returning URLs that implemented searching, buying, and selling. The URLs and their parameters were easily reverse-engineerable from the web Auction House's javascript.
I had to log in to that account once or twice a week to manage inventory space, but other than that it was autonomous. My trading account was flagged only twice - once because I mailed a large amount of gold to my main character, and once because I intercepted some items that a gold seller was using to launder hacked gold.
In short, Blizzard's involvement with their economy is entirely focused on policing RMT. They don't care how players manipulate markets.
