Hi Jon,
A. tuberosa, also known as butterfly milkweed, is not harmful to monarchs. In fact, I often recommend it in urban plantings over common milkweed, as it is more visually appealing and less unruly than common milkweed and an equally good food source for monarch caterpillars. Butterfly milkweed is one of my favorite plants, as it is an amazing nectar source for hundreds of species, including monarchs. One note, however, is if you are rearing monarchs inside, you should continue feeding them whichever species they are on when you find them outdoors. Forcing a host switch can be harmful to the butterfly.