In the long run, no. Bitcoin is still a really good idea, and if satoshi dumped a couple million BTC, the market would absorb them. Sure, the price would drop, but given time, it would also recover because there is value in the very idea of Bitcoin.
The same would be true once Ripple was open-sourced.
Let's wait till OpenCoin opens Ripple and see if it truly becomes decentralized, then there might be ways in which it could complement Bitcoin. Right now, it doesn't.
Is Mt Gox helpful to Bitcoin? Is it open source? Is it distributed?
No, it isn't open source. Helpful is questionable. Distributed, not exactly, but if the question is "are the BTC exchanges as a whole distributed?" The answer is not as much as we'd like, but a hell of a lot more than Ripple. And in the several years I've been involved with Bitcoin (and using it all the time), I've never once used MtGox.