Should I report someone for playing two characters at once?

[Reinha]

Does him multi-boxing badly count, or is that some sort of grey area in terms of a player's skill. I mean, at what point can I claim that he's intentionally disrupting parties when, besides him abusing the vote kick, he just looks like a new or very inept player? I mean honestly if he didn't tip his hand that he was controlling both of them through how he types in chat, then I would still think that it was just the Summoner doing "absentee play."

That's up to the GMs in the end but if you feel like you were disrupted reporting only costs you a little time. Personally I've reported someone for that only once. It was a healer who kept joining our party-in-progress after getting kicked multiple times (it happened before the patch where rejoining a group that kicked you was made impossible). He would refuse to move his character from the entrance so we couldn't progress or get a replacement. It was clearly intentional and completely prevented us from progressing the dungeon so I had to report.

If a player at least performs some character abilities central to their role and moves with the group that's enough for me to not report them (kicking is a different matter). However if I can clearly tell that someone does not intend to finish the duty they queued for and is trying their best to prevent whole group from finishing it then I will happily report that person.