AMD does not provide any binary "Catalyst" driver for Solaris, so the xf86-video-ati driver is the primary option for those using Radeon or FireGL hardware. Earlier this year though, the RadeonHD driver was pulled into OpenSolaris for SXCE, SXDE, and Project Indiana. The RadeonHD driver in OpenSolaris is an option for those using Radeon X1000 "R500" or Radeon HD 2000/3000 "R600" graphics processors.
Version 6.8.0 of the xf86-video-ati driver was released back in February but it takes the OpenSolaris community some time to adopt the changes. In this new release, the open-source driver adds initial R500/600 support, all included drivers now use libpciaccess, restructuring of the ATI wrapper, initial Render acceleration support for the R300/400 GPUs, and an array of other improvements.
Other X-related changes in OpenSolaris can be found in the Solaris Nevada b80-89 change-log. The SXCE Build 87 release announcement can be read at OpenSolaris.org.