Mateo wouldnt fix a problem in the halves. Mateo is a special type of player, where they dont really follow specific position guidelines. You could put him at 5/8, but he wouldnt exactly play the game 'like' a 5/8.
To fix our halves problem, we need a halfback who is consistent, and can take pressure of Mullen, especially in the kicking game, I cant see Mateo doing that. Scotty is the player who can take the pressure off the kicking game, however he is too much of a liability in defence, and isnt much of a threat running the ball. Ben rogers is the opposite, sound defender/good running but doesnt have good enough (or consistent enough) kicking game.
I think all it would take to solve the halves problem, is a jeff robson, scott porter mold player. Someone who can easily give 25 tackles a game (without missing many), provide good support in the kicking game (in porters case excellent), and wont break the bank with their salaries.
Might be worth taking a punt on young Marc Herbet if the raiders choose to keep McCrone over him. From what ive seen he is a decent defender, and isnt afraid to rack up the tackles. Havent seen too much of his kicking game though, as Campese pretty much dominates that, but the raiders seem to always score from kicks against us.
Another option is too take whoever the eels discard out of Jeff Robson or Kris Keating, as long as they can keep Mortimer, they will no doubt have to get rid of one of them.