The answer to this question is "sort of yes" and "sort of no." A single Facebook user can use AppDog on more than one device. For example, if you have an iPhone and an iPad, you can use AppDog on both. However, you cannot earn Bones more than once by installing the same app on each device. To illustrate, let's say that you are using AppDog on your iPhone. You earn 10 Bones for installing GroupMe. Then, you login to AppDog on your iPad. You see the GroupMe offer again. When you click it, you will get a message saying "Offer no longer available." We enforce this policy to assure our advertisers that they are not paying more than once to acquire a single new user.
You might reasonably ask, "If, after installing GroupMe on my iPhone, I can't get credited for installing the app on my iPad, then why does AppDog show me the offer at all?" We are working on it. We will try to have a fix soon!
Note: If you have one Apple device and one Android device, you can use AppDog on both without any restrictions.