Well after playing with this in GGMax, Finally was able to import the hud as DBO. I used the bare hands folder as a template at its default settings.
Setup a map and set the weapon to the player in FP.
Placed a zombie at some dist in one direction, set the armed response guy in an other direction.
Press test game.
The shield hud animations are working and the shield is with the hands. Gunspec.txt settings need to be adjusted for position (Typical weapons setup).
Play results:
The gun with the gun or that type of weapon, can damage me thru the shield. As I would expect. Went looking for the blocking command, and could not find one. Used to be right mouse button in FPSC, But I dont recall this for a long time now.
Now the interesting thing with the zombie was that it could not damage me at all.
Research into the gunspec files may yield further clues to this.
So I would not say that what you are trying to accomplish is impossible, just maybe the physics system is not set up in this fashion to work with the player hud controls. I am guessing from a non programmer POV that the player HUD is always using ray-casting of some sort to do what it does.
Intel(R) Core(TM) i9-10900 CPU @ 2.81GHz, 32GB RAM, Nvidia RTX 2060 super 8gb, Windows 10 Home 64bit, Screen resolution 1920 x 1080
Intel(R) Core(TM) i5-8400 CPU @ 2.81GHz, 32GB RAM, Nvidia gtx1050ti 4gb, Windows 10 Home 64bit, Screen resolution 1920 x 1080. System Passmark 3774