I would not swear my life on it. Biology, hence life itself, is never perfect. A few molecules of ethanol could get produced.
If your yogurt started bubbling with carbon dioxide and smelled funky, throw it out!
The American yogurt industry has exploded in the past few years and people eat tons of the stuff for its protein, calcium, and other benefits. I'm sure those companies' micriobiologists have perfected the art of making safe yogurt. And they're only doing what you're doing but on an immensely larger scale.
The pros exponentially outweigh the possible con. If you feel weird about it, make DIY cottage cheese. That's what I do! I can't eat yogurt... its a textural thing.
All the best!