How do custom pixels use server-side customer events?

[Chris_Sydney]

Hey, 

I know this might be pretty obvious, but I was wondering if custom pixels are using serverside customer events or if these are loaded onto the site as JS? 

For context, I am looking at aggregating collected pixel data across apps (meta,google,klaviyo), and firing those events via server-side to reduce pixel load (via a CDP/Data-warehouse). understand some of these are serverside as well, but things like microevents warrant the need for onpage JS as well, which this looks to eliminate. 

has anyone gone down this path?