Yes, the ID's are somewhat random for the drakes and other summoned creatures. There are specific fields in the GUID that are asserted or deasserted depending on different conditions but in general there isn't any way to determine the 'owner' unless there is an entry in the combat log.
For example when I cast shadowfiend, an entry in the combatlog is written that is able to be used to link my GUID to the shadowfiends GUID.
3/17 17:55:52.812 SPELL_SUMMON,0x0000000002AF70C8,"Tyrala",0x511,0xF130004CD401ACD2,"Shadowfiend",0xa28,34433,"Shadowfiend",0x20
No such entry is created when you fall from the platform onto the drakes during the malygos encounter, so the only way to link the two entities is to save that information during the encounter using the raid tokens and an addon.