Sara -
It is my understanding that males of the same species will fight and one will lose (i.e. be killed). This also extends to those simillar in appearance, but not to the same extent (I have a male Solar wrasse that was being picked on by a Mystery wrasse, but I believe that was more a territorial issue than color - the Mystery was in the tank first). For example, I have heard of people keeping both Linneatus and Rhomboid wrasses in the same tank, but I have also heard these two will fight if territories are not large enough. That said, it is often difficult to tell with some species (particularly the Labouti) which is male and which is female.
The reason to keep them in pairs is so the Male/Supermale (if you can get a Supermale) will retain it's beautiful coloration. Without a suitable female to show off to, a lone male may fade a bit over time. Another reason for me is that I like to see the sexual dimorphism(sp?) between males and females of the same species.
With a 225 you should be fine putting several pairs of wrasses in together. With enough rockwork there will be plenty of caves/holes/hiding places for each to call home. I would look for some with differing coloration (DeltecRules choice of the Labouti and Linneatus is a good one - close in color, but slightly differing body shape and attitude) in an attempt to keep aggression levels and stress down.
For more information on wrasses, speak with Jeff @ Deepreef. He is by far the most knowledgeable fish guy (especially wrasses) that I have encountered and is happy to provide as much information as you could want.
