Nicky has never been to a dog park or on an off leash hike and I wouldn't ask him to. He has been on walks with on leash dogs at the dog beach in Huntington Beach and he is fine as long as he has his space. He likes his space and on leash walks allow me to provide that for him.
Rally has been to dog parks and could probably tolerate an off leash hike fine as long as her daughters were not present and the dogs were respectful of her seniority. As Rally has aged, she prefers only to interact with dogs she knows but she doesn't start trouble either. Rally is fine on on leash walks and hikes.
Rio does not enjoy dog parks but does like off leash hikes with other dogs where it is easier for her to choose not to interact. Like her mother she prefers to limit her interactions to a small group of dogs she knows. Rio is also good on leash for walks with other dogs.
Sophie enjoys other dogs in most situations. She interacts with lots of dogs and enjoys play. She does well on leash but can become frustrated at not being able to do what she wants.
So, if your dogs have no prior experience, I would say if it is an on leash hike where you can control the interactions with other dogs and give your dogs space then they would probably be fine. Off leash, IME, many older basenjis prefer their space and expect a level of maturity that many dogs don't seem to possess.