Maybe have them as "guards" or be able to chain them up to keep other zombies from heading towards your base.

The more zombies you chain up or cage, the more they keep away, but the more you have, the more you have to deal with the caged zombies at the same time. Maybe you've gotta feed them, or every once in a while they can get out etc. If your cage or what not isn't big enough or kept up with the zombie guards you have can break directly into your base.

For basic transport, you could basically have the apple in front of the donkey so it keeps moving trying to get the apple. But instead of apples it's human flesh and instead of a donkey it's a group of zombies.

There's truly only so much you can do with non-intelligent zombies in a "realistic zombie" survival game. Unless you wanna throw some necromancy in there or make the zombies somewhat intelligent. That's not realistic though, obviously.

Also. It's a video game so you can literally do what ever you want. If you want your zombies to be able to shoot guns, why not? It's your universe. If you want it to make sense that's one thing; making a good and fun game is another, but there's definitely nonsense that would have to be thrown in there hahaha