That's the expected behavior. When you reboot the control domain, guest domain will go in freeze since all i/o ( disk and networking) will be coming from control domain. As soon as control domain comes up, guest domain i/o's will resume.
That's correct. Oracle VM Server for SPARC is architecturally different than most x86 virtualization technologies in that, rather than a host/guest Dom0/DomU arrangement where taking down Dom0 also takes down the DomU's, every domain (even the primary/control domain) is essentially a "guest". The control domain is basically a guest with special SW & HW privileges to perform the role of the VMM (Virtual Machine Manager).
This is accomplished by the fact that sun4v SPARC servers include the hypervisor as part of the platform, delivered with the firmware, and loaded before any guest OS instances (including primary).