no, pH is mostly affected by mineral content, and NPK are only as "balanced" as your plants and feeding routine make them, worms will have no detrimental effects ... providing lots of organic material to your garden is the way to insure a healthy soil, which is primarily feeding the microbial population - any type of worm will stay where they have enough to eat, few gardens provide enough to keep a large population of worms happy, and the worms might be better used in a contained composting system, producing castings for addition to the garden

Bill