It has exactly the same meaning in English - "Have we met before" means "Have we met each other before" just as it does in Danish - but it's an active use of meet.
Passive would be "Have you been met by me before?"
"Vi ses" and "see you" are also active. Again, the passive form would be "we will be seen by each other"
Both of those passive forms are obviously very clumsy and would never be used, but my only point was that it was strange to throw in an active verb use in an exercise designed to practice the passive.
@Xneb, are you sure about that? I don't think this has anything to do with the passive voice, this is s-form reciprocity. Do you agree? If so I think your last statement is misleading