Chances are it will be safe if the 2 machines are the same architecture eg sun4u which almost all current sun machines are except for the T1000/T2000.
It is possible the machine you are moving it to has stricter minimum solaris version requirements than the original. But even then you should be safe as long as you patch the OS up to date before moving it.
You should do a "boot -r" on the new machine when you put in the disk.