The main speculation was never Jimmy Olsen, it was Nightwing and some others like The Flash. Here's a wiki link on Nightwing and down from there is the excerpt I quote:
http://en.wikipedia.org/wiki/Nightwing#Animation
"Nightwing appears in the 2010 direct-to-film animated movie Batman: Under The Red Hood, voiced by Neil Patrick Harris. He first appears to patrol Gotham alongside Batman, offering help when he found him fighting a group of smugglers. He was also present during one of the first battles with the Red Hood (Jason Todd), where he obtained an injury to his leg causing him to sit out of the final battle between Batman and Red Hood."
Probably they decided to give Nightwing some more "oomph" by expanding that concept of the leg injury. He's the bionic Nightwing with super-legs that his billionnaire pal Bruce originally paid for perhaps. State-of-the-art upgrades ensued, maybe even with anti-Kryptonian tech just in case.