If not, what do they use. Please provide a source.
Some of the OpenSolaris 10 source code is publicly available, and yes,
Looking at the Debugging With the Kernel Memory Allocator pages from the Oracle Solaris Modular Debugger Guide for Solaris 11 (Express), there is no reason to believe that the allocator changed substantially in that release.
Solaris 10 and older definitely use the SLAB allocator.
OpenSolaris releases, OpenIndiana/SmartOS/etc Illumos based Oses and (current) Solaris 11, i.e. SunOS 5.11 based OSes are still using it.
VM2, an unreleased project, might eventually replace it in a future Solaris 11 version (or not).
Should you want to check is slab is still used in your Solaris release, you can use this command: