White Industries ENO on a Hope hub There seem to be two approaches to single speed freewheels:

Screw on to the hub a combined freewheel/sprocket combination (eg. White Industries ENO)
Slide on a single sprocket to an existing splined freehub body, and use spacers to correct the chainline

I have the former (KT-SY1F / KT-MX7R 6-Bolt Disc hub, Shimano SF MX-30 16T), but I am thinking about upgrading my wheels.
But most high-end hubs (eg Hope Pro 4) appear to come with a splined freehub body. Are these compatible (or can they be made to be compatible) with the screw-on freewheel/sprocket combo? If so, can the chainline be corrected for in this configuration?
No, there's no way of getting a singlespeed freewheel onto a cassette hub or a singlespeed cassette cog got onto a freewheel hub. ENO freewheels mostly exist to provide a high-end, high engagement rate option for hubs and trials cranks that need a singlespeed freewheel.