The only thing I can't stand about dual accounts is if someone uses them to spy. Then again, they are paying for it and it isn't against any terms of service. So, I guess what I am saying is I wouldn't do it and won't fly with people that do (if I know).
However, if someone is doing it to get more varied pratice in an MA environment, well, weird, but OK. It is a better alternative that the offline-fly-in-a-circle option.
And if someone is such a score (or perK, if you notice the rides used) freak that instead of earning them, well, that's sad, but again they are paying for it. Let them do it...take note, make sure people know, but let them have there score-padding-perk-padding-look-how-awesome-I-am-I-R-L33T fun.
As a side note, I make it a practice when flying on a missions with the squad not to announce objectives and or goon status.