How does the Salt March explain whether or not Gandhi's plan for non-violent tactics was successful?

yes. it was successful.

Explanation:

Gandhi choses to remove the tax from salt in non violent form. so he decided to approach satyagraha movement which is also know as Dandi March. the march, thousands of Indians followed Gandhi from his religious retreat near Ahmedabad to the Arabian Sea coast, a distance of some 240 miles.