Yes, they can. The number of the gang members in both gangs is not a major factor in the City Kings matchmaking. Otherwise, gangs with few players would have a real problem finding opponents every day.
Please note that there many gangs out there that have 25 players, but only half of those players are active. The system can't predict which and how many players  in each gang will decide to join the attack, so the numbers don't hinder the matching if the other factors are right.