Here are 4 ways to know which ped is what (2 of them for grapplers and strikers and 2 for all of the ped kind)
(1) To know for example which prep/s is P_Grappler_A , Just edit their health and get ig and fight preps till you find them.
(2) This is a way to know which are which WITHOUT editing the pedstats.dat file. for example : P_Grappler_A - Just go in game and fight preps , now back off from the prep while fighting and shoot them with a small shot with your slingshot (make sure they dont fall from the hit) then they will run towereds you to attack , if they grapple you , then they are grapplers. If they punch / knee you then they are strikers , melees, or Ranger (not sure about the ranger)
(3) I will update my pedstats.dat tutorial and will write which ped is what in pedstats.dat for better explanesions.
(4) Some of the peds (for example Juri , Hal and Norton) use special grapplers ( bear hugs and some WWE style lifts and drops) , they are usually grapplers (Except for Russell in free roam , he is not a grappler , Russell is a grappler only in his boss style stat)
Note : Remember some of the pedstats.dat names are used by a few peds. for example : G_Striker_A