The 6-foot-11 Plumlee signed a four-year, $50 million deal with the Bucks during the summer but hasn't received steady playing time. He has played in just 32 games with 12 starts, averaging just 2.6 points.
"We are excited to add Miles to our roster," Hornets general manager Rich Cho said in a statement. "He is an athletic big man who brings additional physicality and rebounding to our frontcourt rotation. He's a proven player with a strong work ethic and we think he'll fit in well with our core group."
Injuries have slowed Hibbert this season, and recently he had fallen out of coach Steve Clifford's rotation as the Hornets have tried to shake out of a slump. Hibbert is averaging a career-low 5.2 points and 3.6 rebounds in 42 games. He signed a one-year, $5 million deal with the Hornets last year.
Hawes is a veteran shooting specialist. He's averaging 7.3 points and 4.2 rebounds in 35 games but is shooting just 29 percent on 3-pointers, his lowest in seven seasons. He has a player option in his contract next season for $6 million.
"Spencer and Roy are two proven NBA centers who give us additional depth and versatility in the front court," Bucks general manager John Hammond said in a statement. "The trade also gives us future cap flexibility as we continue to shape our roster. Miles and Steve [Novak] are true professionals both on and off the court, and we wish them all the best."
To make room on the roster, the Bucks waived Steve Novak.