I meant the King and Rebel relation, not the lineage of the Camerans.
In that case, from what I've seen, many of those who would be considered Rebels gain, through successful warring, enough of a claim to ruling Cyrodiil that the Amulet can be worn by them (as a claim to the throne seems to be the prerequisite for being able to wear it). At the same time, however, it isn't the only way to wear the Amulet, as some (and in fact probably most of those who've worn the Amulet) can gain claims to the throne without trying to usurp the current King.
Edit: The main confusion on wearing the Amulet, both on the Forums and in Cyrodiil, seems to come from the fact that the vast majority of those who've been able to wear the amulet and actually do so were descendants of the previous rulers.