> are these TWO cards the ONLY AtomBIOS-based Radeon cards that can be used
> with MorphOS?

http://www.morphos-team.net/hardware lists 9 supported AtomBIOS-based R5x0/RV5xx cards (Radeon X1300 to Radeon X1950 Pro).

> How can you actually tell that a graphics card is AtomBIOS-based?

AtomBIOS is used on every Radeon graphics card based on R500 or newer GPU series* (so Radeon X1300 and newer cards), except the X1900 GT variants with PPC ROM.


Edit: * While early AtomBIOS versions came already somewhen during R400 series, the MorphOS AtomBIOS parser seems to require the newer AtomBIOS versions that started with the R500 series.

[ Edited by Andreas_Wolf 19.01.2021 - 00:58 ]