If memory serves, the virus was created by a crazy French scientist who defected to the Viet Minh in 1954 and saw it as an opportunity to get back at the West,
There was Jungle Jim's commander, who could somehow command the undead.
As well, there was a undead Marine who could fire his M60 accurately.
I think the VC zombie with a scythe was a modified one by the crazy VC scientist rather than a Rememberer.
The 68 zombies were just a slight tier above the zombies in Walking Dead. I recall 2 scenes where walkers used bricks to break glass and Morgan's wife remembering the house where she died.
Spoilers for '68 which I just found out about and binged.
The virus was the result of spice 68, a food preservative that was eventually used globally. Normally harmless until Earth waded into the radiation from a comet trail that turned the preservative into a zombie virus. "We are what we eat" and all that. The body rots, but a portion of the spine takes years longer to rot. The zombies don't see or hear, their eyes turn amber, but they can still sense humans - heat or some other thing.
The scientist was a guy whose wife - a Soviet leader's daughter married off - that got burned alive in a bombing. She survived with full body burns long enough to make it a hospital. He smothered her and swore vengeance on the US. When the dead came back he found a away to stimulate their electrical nerves to make them run and jump on command via radio. Made dozens of them for the VC to attack Saigon during the outbreak. He gets killed later on.
The commander 'taught' zombies like how'd you teach a dog. Don't bite him, you get a snack. Snap at him, you get beaten. He captured hundreds of zombies as like an honor guard to lead a swarm of zombies against a group of survivors in Vietnam. They get bombed.
The undead marine with the machine gun got tangled in vines so less accurately fired and he tried to get food and his finger pulled the trigger till he spent all the bullets.
I'd say 68 zombies are a tier below WD in that they don't have a 'evolution' in what they do, but their behavior can be modified.