RPPvP : What is it and do I have to?

RPPvP refers to the type of interaction between characters that results when you combine roleplay with player-versus-player. This means taking duels, arenas, battlegrounds, or world PvP ICly and acting accordingly. Often RPPvPers will not RP out fights with emotes; generally skill in PvP is preferred to the luck of roll-based fights.

Do you have to? That entirely depends on your rank and character concept:
Contenders and Champions are expected to RPPvP. The events that are staged are based on it; the control they exhibit shows their mark not only as skilled PvPers but as being true to one's character. There is no control in an RP fight, not when you're using a roll system, and RP fights are usually extremely boring to watch given the length of and length between posts. So, as a contender or a champion, yes you will be expected to participate in RPPvP.

If you are another rank? You will not be forced to, though if you choose to participate in any tournament fights you will need to. As well, if you ICly challenge one of the people within RPPvP ranks you can expect a flag duel.