URL-scheme details for Reminders application
I don't know the details of URL scheme.
However the scheme is x-apple-reminder not reminders
It can launch reminder app at least. 

However the host and path rule is not revealed yet.
Reminder widget can open Reminder with specific EKReminder, 
So, there must be a scheme definition for it.

The scheme x-apple-reminder is undocumented, So using it should be rejected.