Hello,
On the Solaris OS, WebSphere installs the IBM Solaris Hybrid SDK. This SDK contains the hotspot VM, the Java 6 class libraries, and some ibm extensions under jre/lib/ext and jre/lib/endorsed. IBM doesn't have it's own VM on Solaris.
You can check which SDK was shipped with each WebSphere release here:
http://www-01.ibm.com/support/docview.wss?rs=404&uid=swg27005002