Najera averaged 5.9 points and 4.3 rebounds a game for Denver in the 2007-08 season. He has also played for Dallas and Golden State during eight seasons in the NBA.
Hayes, a five-year veteran, averaged 6.7 points and 2.2 rebounds for the Detroit Pistons this season.
"We are very pleased to add two veterans like Eduardo and Jarvis to our roster," Nets President Rod Thorn said.
"Both are solid, competitive NBA players who will add versatility and depth to both our front court and back court rotations."