Yes,
The character's FPI script would have a healthless=X condition which cause a plraddhealth=x action when true.
For instance, if we were using the shootclose.fpi for the character then we would add the following changes. (backup a copy first)
Add the following four lines just below the ;Triggers header as shown in this...
;Triggers
:healthless=20,activated=33:activate=34,plraddhealth=20
:healthless=40,activated=32:activate=33,plraddhealth=20
:healthless=60,activated=31:activate=32,plraddhealth=20
:healthless=80,activated=9:activate=31,plraddhealth=20
Then add activate=9 to state=0 as shown in this...
:state=0,plrcanbeseen:activate=9,state=1,settarget
:state=0:runfpidefault=1
Now, using the method above he won't give you any gains unless he sees you, and then you gain 20 for every 20 he has lost.
If you change the placement of the activate=9 in state=0 as shown in this...
:state=0,plrcanbeseen:state=1,settarget
:state=0:activate=9,runfpidefault=1
Then you get a GOD effect (fills you health up) if he takes 20 loss and doesn't spot you.
Otherwise, you gain 20 for every 20 he loses if he has spotted you.
You could apply this to just about any character's AI.
Have fun
