I thought succulent referred to any plants which are like cactus, but without spines. I would assume that on the hoodia bottle they meant whole plant (as opposed to an extract). But I'm not an expert...
EDIT: Okay, looked it up. Cacti do fall in the succulent family. Therefore, all cacti are succulents, but not all succulents are cacti (examples of non-cacti succulents are hen and chicks, aloe vera, etc.) Also, the spongy tissue of these plants which is used to store water is known as succulent tissue. So, my assumption still stands.