Nice question. In the google documentation “Unified Schema” I think they speak about Measurement Protocol v2
And here is an example of sending a request to GA using it
Even in case, I am wrong and “Unified Schema” is some other object. You can use Measurement Protocol v2 and sendHttpRequest function Server-side tagging APIs | Google Tag Manager - Server-Side for sending data to GA.
If you find out what exactly “Unified Schema” is, please send the info here.