I think this should be in the mapping forum. Anyway, in Hammer, it's the same entity as the normal Combine soldier.
npc_combine_s
Once you've created the entity, browse through the paramaters. One of them is "Soldier Type". You can choose from "Normal Soldier", "Prison Guard" and "Elite".
Too bad they dont let you tweak more settings with the NPC In Unreal, you can set their health, their skin, their ai pattern, their relationship, loads of stuff.