relocating, not kidnapping
here's the legal definition
http://legal-dictionary.thefreedictionary.com/kidnapping
Here is the relevant part
Generally, kidnapping occurs when a person, without lawful authority, physically asports (i.e., moves) another person without that other person's consent, with the intent to use the abduction in connection with some other nefarious objective. Under the Model Penal Code (a set of exemplary criminal rules fashioned by the American Law Institute), kidnapping occurs when any person is unlawfully and non-consensually asported and held for certain purposes. These purposes include gaining a ransom or reward; facilitating the commission of a felony or a flight after the commission of a felony; terrorizing or inflicting bodily injury on the victim or a third person; and interfering with a governmental or political function (Model Penal Code § 212.1).
So explain to me how it isn't kidnapping?
Well in the UK
Kidnapping is an offence created by judges in the seventeenth century. The current definition is that kidnapping is an attack on or infringement of personal liberty, consisting of the taking or carrying away of one person by another, by force or fraud, without the consent of the person taken or carried away, and without lawful excuse.
http://lawcommission.justice.gov.uk/areas/kidnapping.htm
So lets break it down
attack on or infringement of personal liberty, consisting of the taking or carrying away of one person by another
They were intending to carry the Ba'ku away.
by force or fraud
They were going to use a holoship to make them think they were still on their planet, sounds like fraud to me.
without the consent of the person taken or carried away
The Ba'ku weren't asked if they minded being moved
and without lawful excuse
Whist the planet might be within Federation space, it was settled before the Federation was founded and the Ba'ku weren't informed so they could seek redress through legal means.
Looks like the criteria has been meet.
And you don't need the ransom part, if you grab someone of the streets and move them 10 miles from that location and let them you go, you are still guilty of kidnapping. As that person did not give you consent to be moved.