Aggression is an all encompassing term. As pointed out above, there is quite a range! It is not unusual for Basenjis to be dog aggressive. Mine is, and I just avoid other dogs because I know his intentions are not good. Some are same sex aggressive and fine with members of the opposite sex, and some may just be making a statement when they are leashed. If you describe what you are seeing more specifically I am sure lots of people will have common experiences and possible training fixes to share.
I would love to see some pictures of Tucker, and welcome to the forum!