Aminu, 23, spent the past three seasons with New Orleans and averaged 7.2 points and 6.2 rebounds in 80 games in 2013-14, starting 65.
He played his first season with the Clippers after being taken with the No. 8 overall pick of the 2010 NBA Draft and was traded to New Orleans as part of the package that sent Chris Paul to Los Angeles.
Aminu owns career averages of 6.5 points and 5.5 rebounds in 303 career games, including 171 starts, with the Clippers and New Orleans.
Johnson, 30, began his professional career in the NBA Development League and averaged 6.5 points and 3.9 rebounds over 125 games with the Atlanta Hawks from 2011-13.
He spent the 2013-14 season playing in China and started all five games for the Mavericks at the Las Vegas Summer League this month, averaging 7.8 points.