The answer to this query is based on what you are looking for in a bittering agent. Angostura bitters are hugely popular for their classic cinnamon-almond flavor, making them an excellent addition to a number of cocktails, from Old Fashioneds to Manhattans. However, Campari has a distinctively fruity and herbal profile that will add complexity to your drinks in a way that Angostura bitters cannot match. For this reason, it is often recommended that you use Campari as the bitter element in an amaro cocktail or even as an ingredient in your own homemade amaro blend. That said, if you are simply looking for something with a rich and complex flavor profile that complements other ingredients, then Angostura bitters may be just what you need. Ultimately, whether or not you can use Angostura bitters instead of Campari depends on the specific drink that you are making and the characteristics you want to bring out in it. So experiment with different ratios and explore all of the potential combinations! After all, the only method to know for sure is to try it out yourself.