Is there a reason you aren’t using the built in JSON parsing library in the engine? I use it and it works well.
See: https://docs.unrealengine.com/latest/INT/API/Runtime/Core/Serialization/Json/index.html
If you really want to include an external module, check out these options:
In general, when including modules, take a look at like “Engine/Source/ThirdParty/libPNG/” and the “UElibPNG.Build.cs” file in there, it shows how you can include a totally external module. There are lots of other examples in the ThirdParty folder you can look at.
Alternatively you can look at making a plugin, there is some info on plugins here: A new, community-hosted Unreal Engine Wiki - Announcements - Unreal Engine Forums
Hopefully one of those options will help you.
Joe