Is it safe to grow vegetables in Miracle-Gro soil?

Absolutely safe -- nothing to worry about if you want to grow tomatoes, peppers, carrots, spinach, whatever in commercially-prepared potting soil such as Miracle-Gro that already contains fertilizer. Once fertilizers have broken down into their chemical constituents of nitrogen, phosphorus, potassium, etc., and are inside the plant's tissues, it makes absolutely no difference whether they originated from composted manure or chemical fertilizers such as ammonium nitrate. (Anyone who tells you differently is not telling you the truth, but instead merely expressing their own unscientific biases and prejudices -- ask anyone who says so to show you proof in a Botany or Horticulture book.)