That depends on what “premade” means contextually. If you mean multiple groups, then no. If you mean full groups, I don’t know for sure, and I don’t know what happens if the opponent team has no groups. Regardless, my feeling says that this matchup isn’t working properly.
I personally would like to see Battlegrounds that have more than 2 teams. Either PvPvE of which Horde and Alliance have to fight a 3rd PvE faction at the same time (Epic Battleground), or we ditch Horde and Alliance and just make mixed teams in a map where 3 or more factions at the same time. While this would still be an Epic Battleground of players, they’ll be in different teams.