Health values are exactly the same, with the occasional exception.
e.g
NSF
Vanilla: 75hp per body part on all difficulty levels
GMDX: 75hp per body part on all difficulty levels
Enough for one headshot to kill, excluding the assault gun and melee weapons.
MJ12 Commando
Vanilla: 150hp
GMDX: 250hp
Why is this? Well first of all the commando is a from head to toe fully armored cyborg, so that's the "teh ultimate realism at all costs!" faggots covered. Second is Deus Ex got ridiculously piss-poor easy about half way through the game. First half could be rather hardcore to the uninitiated with the accuracy system, health system and such, while the second half was one shot mole pops. The misconception that bullet sponges are inherently bad is hilarious, especially when you have believable excuses for it (helmets, ballistic vests, full body armor, ballistic protection augmentations, re-routed fear of pain). Games are full of sponges, and for good reason. Without it the experience can easily become:
Bullet sponges in moderation aren't a bad thing. Doom and System Shock, the two early templates, were packed full of bullet sponges.
Deus Ex's accuracy system went some way to not make it a case of simply pointing and clicking at heads to one-shot mole pop while also including a semi-realistic health model, but once you got remotely skilled the need to add spongeyness was a must. Vanilla the most HP an enemy had was 350 (MiBs), which was enough to take SIX untrained stealth pistol headshots or FIFTEEN untrained assault gun headshots. It didn't even try to explain it away by giving MiBs armor or ballistic augs.
So in short, while GMDX buffs enemy hp here and there to provide better gameplay it never really goes past that standard of semi-realism. Hardcore mode is an exception, but not by much. Every enemy with high hp has semi-believable armor protection accompanying, often added by GMDX.
GMDX makes such aspects more realistic, for example MiBs now have subdermal BP-implanted skin as evidenced by the sound it makes upon bullet impact, and helmets now deflect bullets and can also be shot off of heads. Headshot collision issues are fixed. Hitting the enemy in the back of the head counts as a takedown and so on and on.