Emudev is largely a hobby field. It takes skills from many fields to accomplish. You need the combined efforts of hardware engineers, reverse engineers, diligent documentarians, software engineers with specialized skill sets, etc. Everyone building on top of each other.
You'll see one-person operations, but they're usually relegated to older hardware and they still utilize documentation from many disparate sources. Even nesdev wiki was built on top of 6502 researchers, Taiwanese clone manufacturer reverse engineers, decappers, older NES emulators, heaps of existing documentation, etc.
There are many jobs for emulation development though. Every company that makes chips has an interest in having software emulators of them since it's easier to try out a new feature in an emulator than to write it in hardware. For example any GPU maker (AMD/NVIDIA/ARM/Qualcom/Imagination/Apple etc) will have a team of 10-100 people working on one or several emulators for their products.
You'll see one-person operations, but they're usually relegated to older hardware and they still utilize documentation from many disparate sources. Even nesdev wiki was built on top of 6502 researchers, Taiwanese clone manufacturer reverse engineers, decappers, older NES emulators, heaps of existing documentation, etc.