I don't think it'll cost us promotion, but continuing to unbalance the team by playing Hoolahan down the left will certainly cost us points. Constantly drifting inside will focus our attacks down the right, and with no left sided width to speak of, the opposition defence can double up on Redmond easier.
With that in mind, it becomes a case of losing some of the effectiveness of other players, as well as Hoolahan.
It's always been a feature of his game that the positions he occupies and the things he tries, he loses the ball a fair bit. When he has the ball down the left and loses it he only really has Olsson for cover, and if he's overlapping then then the three remaining defenders have to get across to cover. Not ideal, especially as hoolahan doesn't really have the pace to make up for his mistakes. Lose the ball in the number 10 "hole" and you should, in theory, have 2 or 3 players around you to win it back.
Play him as a number 10 in a 4231, and make the hard choice about which of the strikers you're going to play. It's rarely a good idea to make certain players undroppable and play them in the wrong system.
Just look at Welbeck at the moment, for a slightly different example. Roundly abused at Utd for being crap, but never played up front because Rooney is untouchable, despite his tendency to completely unbalance their team by getting himself out of position. He's now being played in his correct position and Arsenal seem to be getting the best out of a player that most people thought wasn't worth 16 quid, let alone £16m.