> are there any R200 card, with memory 256 MB visible on MorphOS?

Existence of R200 cards with linear 256 MiB aperture was confirmed no later than 2010 (#3, 2nd link therein (#65)).

MorphOS 3.0 release notes from 2012 read:
"Enabled full 256MB on cards offering a 256MB aperture."

As this note mentions no restriction to any Radeon GPU generation, there's no reason to assume it not being valid for R200 as well. So in conclusion, since MorphOS 3.0 there're R200 cards with 256 MiB VRAM usable on MorphOS.