There is no direct migration path, you need to go to a 6.X or 7.X before going to 8.X
Table 4 Supported Cisco Unified Communications Manager Upgrades for Release 8.0(x)
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/compat/ccmcompmatr.html#wp184796
If you use DMA and then the Linux to Linux migration all your licenses will be migrated in the process, otherwise if you do a fresh install you need to reach licensing (licensing@cisco.com) so they can migrate the licenses.
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www.cisco.com/go/pdihelpdesk
HTH
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if this helps, please rate