I do think it's something you need to consider. He worked with Patrick Roy. Great, I also think that any player who is legitimately one of the best in the history of the game would probably be that way regardless of who is coach is (assuming the coach plays him) because their own internal compete factor is just on the next level of their competitors. He also had great success with JS Giguere. I don't doubt for a second that he helped revive his career.
But not every coach works with every player. I don't think it is unfair to suggest that Allaire can be a good coach, and a guy who both Reimer and Gustavsson respect, but it doesn't mean that he is the guy who can get the most of these guys. I think he has done some really nice things with Gustavsson in terms of getting him to stay closer to the net rather than going on fishing expeditions each time he makes a save, but I think the style of drop and make the puck hit you isn't ALWAYS the right thing to do.
One thing about Reimer though. Last year, I felt he was really strong at making the 1st save. He squares up to the shooter really well. A big difference between last year and this year is that he is giving up way more rebounds. I found his ability to reset for the second shot, or move laterally is where he can get into trouble at times because he isn't nearly as athletic as Gustavsson (obviously he can still make some big saves like the stick save on Saturday) so it's harder for him to push off and get across the net. I think that is a place where always crouching down does Reimer a bit of a disservice because he's taking away his size advantage and he's not in an optimal position to push off across the net.