Can a necromancer control zombies?

Uh, define "necromancer."

In Voodoo, the Boker can control his zombies. There are strict rules, of course. They can't eat certain things, see things, and so on. If they do, then the zombie leaves their control. Of course, I'm not certain that this is the type of Zombie you are asking about. They are not the flesh eating zombie terror that Romero dreamed up.

The more D&D type, where the necromancer calls a spirit back into a dead corpse is another story. Normally, yes. It requires calling the correct spirit/soul back, or you can't. It has to be a "weak" spirit, or you have a control battle. First, it is going to hate you calling it back, in many cases, to this hell we call life. An evil spirit may be OK, but has it's own ideas. A good spirit, well, you're going to upset it and it is going to resent this call back. The "stronger" the spirit, the harder it is to control. The problem is, not many know how to do this, to begin with.

It's far easier to break control than to establish control.

Working with a hostile spirit is problematic. It isn't one you called, well... Try negotiating. ;-)