Hives count as single creatures, right?
Nanobots as Hives! Perfect.
Swarm = single creature
Swarm + Dark Unity = still a "single" creature
... but the text includes a clause (iirc - i'm going from beep memory)
to treat it as a single creature as often as possible,
but you don't absolutely have to.
Hive
can do a Nanobot type approach, but doesn't need to.
Nanobots could certainly acquire the pieces necessary to do a Hive,
but each individual nanobot would have to be something that could
be in a normal swarm subtype with vermin It's probably much easier
to go Hive into Nanobots , rather than work real hard to go Nanobots into Hive.
Not saying it's impossible.