Yes, they render in a special viewport, not the common way most 3D apps do.
From
http://docs.pixologic.com/getting-started/basic-concepts/the-canvas-document/
ZBrush isn’t quite like other 3D packages because of its 2D elements: it doesn’t have a 3D scene, but rather has a 2.5D canvas document on which you can draw 3D objects. Many of ZBrush’s signature and most powerful features are made possible by the fact that ZBrush uses a depth-enabled canvas rather than a full 3D space.
How they zoom on The scene is also very uncommon due to how their rendering works
The Zoom controls in the Document palette act on the canvas, enlarging the pixols. So if you zoom in far enough, you will start to see the individual pixols and the image will lose definition. It is just like enlarging an image in a photo editor.
When you are working on a 3D model in Edit mode and want to get in close, you don’t use the canvas zoom. Instead you Scale the object. Scaling the object means you’ll be able to get in as close as you want and work on tiny details without any loss of definition. Note that scaling doesn’t change the true size of the object; it only affects how much of the canvas your object takes up.
Zbrush will always stay way faster because it’s a lot more faster and efficient rendering approach.
@TheRedWaxPolice
Do you believe more in what random internet guy says or Pixologic documentation 
BTW, Zbrush is dedicassed sculpting app since long time, Blender won’t become Zbrush until they hire a team dedicaced to scultping.
Meanwhile Blender is already very capable, those needing absolutely sculpting high rez on Blender instead of using Zbrush, have a solution that is invest in a top notch 3D card like Nvidia Quadro RTX 8000, but this will cost lot more than buying a Zbrush license.
