Would I be able to import the backup from a higher license count install of LMS 3.0 to another one with fewer licenses? What potential gotchas could there be even after the restore were successful?
Also, what does it mean "CWLMS-3.0-100-K9" is "not supported" on Solaris? Can it be installed on Solaris at all?
Yes, a backup from a higher license count can be restored to a lower license count. Basically, the license is backed up, and will be restored. The result will be both machines using the same license. You can then clear out the restored license, and put back the smaller license. The net result will be that the devices that exceed the smaller license plus 10% will not be manageable, and you will be nagged until you reduce the managed count to a supported number.
The decision not to sell a 100 device license for Solaris was mainly due to marketing. The problem is with Solaris 10. Solaris 10 has a lot of new subsystems (e.g. SVC framework) which require more memory. The result is that the smallest working Solaris LMS server would need 4 GB of physical RAM and 8 GB of swap. These requirements are ridiculous for managing only 100 devices.
Since there is no license for 100 devices on Solaris, whether or not you can install this license on Solaris is a moot point.