yes, it is my understanding that lemon juice and whey are fairly interchangable but I've not used lemon juice, only whey.
We make homemade kefir, yogurt, & kombucha. I've made my own fermented salsa a few times as well as fermented pickles.
I cannot eat pickles made in vinegar, yuck. I have been meaning to try and catch some wild yeast in a sourdough starter--I've got the rye and everything, just haven't done it yet. When we eat grains, we don't necessarily ferment them, but we do soak them overnight in a kefir or yogurt mixture.