First off - everything is possible in OFP ! You just have to specify how realistic (ie complicated) you want it to be. ;D
For example - I could knock together a script that allowed a unit to pick up a fallen comrade and carry him no probs. The REAL problem is writing the routine and finding the right animation to make it look and feel right.
Try this - put a trigger on the map called "everyone", activated by "anyone present" and make it 10k on a side. Now make a script that runs continuously that checks all units returned by "everyone" (ie - everyone !).
If a character is dead or unable to walk then all you have to do is run a routine that calls in a magic medic (create Unit) or directs the nearest friendly to move to the unit. Once they get there they should do some animation, then either disappear or pick them up and move to some predefined point (perhaps a gamelogic for each side ?).
The picking up bit could be a bit of problem unless there was a good animation that could be used to play on the carried patient. After that, all you have to do is move the helper to the target casualty clearing station and end the routne.
As I said - easy as, you just need to have right routine and the right animation.
Cheers
roni