Chinese farmers etc will not harm the top-end-item economy. They will very likely impact the commodities and gold markets though.

Why? Two reasons.
1) Gold farmers usually use several dozen bots controlled by 1 person as it is too expensive to hire actual people to play the characters themselves. Any bot in Diablo 3 will not work in Inferno (or maybe even hell) due to difficulty and need for quick reactions and skillful play. Writing a bot that can be as skillful as a person is impossible by a longshot. In MMO's its different, the environments are static, the gameplay is slow and its almost turn-based combat. This is easy to code, as you can simply queue up abilities for the bot to use against 1 monster at a time. Diablo 3 is the polar opposite.

2) Chinese farmers are typically not that skillful at actual gameplay. This is because they don't actually "play" the game, they farm the game. There is a big difference. Inferno in D3 requires extensive use of both build skill, gameplay skill AND building up gear progression. This means that Chinese farmers will simply not enter inferno, and instead farm for gold and magics in the easier difficulties.