Currently we don’t have any service (OTTB) for JSON validation. However you can make use of pub.schema:validate, create an IS document from JSON file and use pub.schema:validate to pass the IData to validate it.
Moreover there are public JSON services (pub.json:*) in WmPublic you can make use of them and build own custom logic to validate JSON.
You can raise a Feature Request in SoftwareAG Brainstorm in Empower to request for JSON validation service. Share the request number I can add my vote.
#Integration-Server-and-ESB#webMethods