Sharp, who won the pole at Indy in 2001, has driven in 12 previous races at the Speedway, with a best finish of seventh in 2005. This is his first season with Rahal Letterman, which won the 500 with Buddy Rice in 2004.
"One of the things that attracted me to Rahal Letterman Racing was the team's success at Indianapolis," Sharp said. "I have won races and championships during my career, but the ultimate success at Indianapolis is something that has eluded me."
Simmons, in his second season with Rahal Letterman, will try for his third start at Indy. His best finish was 16th as a rookie in 2004.
The entry deadline is April 4. The race is May 27.