No, you don't need to join a school wrestling team to become a pro wrestler. While wrestling experience is helpful and common among pro wrestlers, it's not a requirement. Many pro wrestlers come from various backgrounds, including amateur wrestling, other martial arts, bodybuilding, gymnastics, and even no prior combat sports experience at all.
What's far more crucial is training at a professional wrestling school. These schools teach the specific skills and techniques of professional wrestling, including the choreography, storytelling, and safety aspects essential for the business.