As far as I know, the IFL has 5 fighters per team. Which means one fighter per weight class. Wouldn't it be a good idea to have second and third string fighters to cover someone's position in case a fighter needs to recover from an injury, similar to the NFL. Just look at the UFC and how many medical suspensions are handed down after an event. I think that a system like this would allow teams to have a full roster, even in the case of a fighter being injured. Is this a good idea or have they already implemeted something similar?
They do.
Every team has alternates. In fact, the alternates alternate fighting on the shows. In Portland, the 185 lb alternates from each team opened the show.
Also, the way the IFL has set up their league is much different from the UFC. They do not allow elbows to the face because if you notice, that is where a majority of UFC injuries come from. The IFL will have their athletes competing on a regular basis, so they are doing everything possible to keep their guys healthy and able to fight. Basically, they are looking out for their fighters.