The reason many people use vodka in their airlocks (including me) is because vodka is basically flavorless, and the alcohol will kill bacteria or wild yeast if they fall in. Once the vodka has been diluted (3/4 oz in 5 gal) that far, there isn't enough alcohol to kill the yeast. RDWHAHB. If there is some problem with your yeast not starting, it won't be because of the vodka.