It depends what you mean by “discoverable.” 
There is a community-created wiki that has “quick browse” lists so you can more easily find custom code (both Groovy DTHs and Edge Drivers) by device class. So there’s a list for lighting, a list for motion sensors, etc.
You should also know that SmartThings itself is in the middle of a huge transition to a new architecture. Sometime soon the free Groovy cloud will be shut down, and all Groovy DTHs, whether stock or custom, will cease to work.
Instead, hub-connected devices will use Edge Drivers which will be written in a different programming language, Lua, and which will run on your own hub.
Zooz is one of the companies already working on creating the Edge Drivers that will be needed for its products, so you should be fine there.
You can see the list of currently available beta Edge Drivers in the same section of the wiki:
But so far very few of the authors of custom Groovy smartapps have indicated that they will be converting to the new architecture, so when it comes to creating rules to operate the devices it’s going to be a whole new world. 
You’ll probably either use the routines creator available in the SmartThings app or, if you need advanced functionality, the new Rules API.
One of the main points of the change to the new architecture is to make it easier for device manufacturers to create and distribute code to expose the full functionality of their devices. So the idea is that in the future, rather than having to individually research and apply custom code for a device like the Zooz scene controller, you’ll just click on a link to subscribe to their Edge channel and you’ll automatically get their latest and greatest code for all their devices.
So a LOT of change is coming, we don’t know all the details yet, but it should make it easier to get full value out of the devices you add to your SmartThings account without having to do a lot of work or research.
Official announcement: