While I do think there were followers who were not technically Death Eaters (as there seems to be now, too... We know of a few people who have followed Voldemort without technically being Death Eaters), I think Lupin was only speaking of the active actual Death Eaters, because those guys were the real threats. It's possible, I think, that there is some sort of hiarchy (:lol: I can't spell) among the Death Eaters, and only the top ones were in the graveyard the night Voldemort returned, but I definately think that there are many more Death Eaters (actual active ones) who were and probably still are a threat to the Order and... well, and everyone.
I think there's plenty of evidence to support this. Karkaroff saying what he did about none of the Death Eaters know the identities of all of the Death Eaters (meaning that they couldn't have ever met with every one of them), what Dumbledore said about Voldemort dealing in secrecy, what Lupin said about the Order being vastly outnumbered, and I really like what pallas was saying about how Voldemort doesn't trust his own men. I think that's fairly obvious, given the way he talks to them, and that old saying "It takes one to know one" could definately be used here. Voldemort gained his power and control because he had a lot of the same qualities as his followers. He knows that he would have stepped on the little people, and eventually the big boss, to get into power, and he knows that it's most likely in their heads to do the same thing. These men didn't become Death Eaters truly to help Voldemort become powerful, they did it to get the power themselves.