"Greg is a big asset both physically and mentally. Having a player with Greg's experience is invaluable for these developing players. I hope that Greg is able to use this opportunity with the Legends to create one more opportunity at the NBA, similar to what Antonio Daniels was able to do last year," said coach Del Harris in a statement.
Ostertag, a Duncanville, Texas native, has averaged 4.6 points, 5.5 rebounds and 1.7 blocks in 756 career NBA games.
Ostertag retired with the Jazz, the team that selected him 28th overall in the 1995 draft, after the 2005-06 season.
The Legends also retained Drew Neitzel, who was waived by the Mavericks last week.
"We're thrilled to add Drew to our roster. He's a great passer and he keeps the defense honest with his outside shot," said Harris.