Configuration: SparcStation elc, 16mb ram, 64mb swap. RH 6.0 plus all updates (XFree86-SunMono-3.3.5-1.6.0); Kernel 2.2.5 or 2.2.10 give the same result. startx, xinit or simply /usr/X11R6/bin/X results in screen simply turning black - no cursor or any other output. ps shows all the expected X processes running (X server, gnome and friends, etc). I can switch consoles with ctrl-alt-F[1-6], however switching back to the X console with ctrl-F7 leaves the old text on the screen (the text cursor disappears). ctrl-alt-backspace exits with the usual "waiting for X-server to shut down" messages. I've tried this with the default xinit setup and also with a minimal $HOME/.xinitrc containing just an xterm, with the same results. gpm is turned off. Xconfigurator exits with messages to the effect that there is an error in my X configuration - this also happened at install time. Sbus bwtwo frame-buffer is recognised at boot time.
elc's with bwtwo framebuffers are fully supported in our forthcoming 6.2 release.