Hm I don't think so, the imperfect tense indicates something that lasts in time; I think "What brought you together?" would be "Cosa vi ha unito?".
Agreed, 'What brought you together?' would be right only to describe the beginning of some kind of relationship. 'Cosa vi univa?' implies two things:
1) what was linking two or more people during all the time they spent together, the common interests they shared;
2) the aforementioned people are not united anymore, otherwise the present tense should be used instead.