First you have to understand that being native to a plane and having the Native subtype are two different things. Every creature is native to a plane, but only Outsiders native to the Material Plane have the Native subtype.
Native subtype, Monster Manual p.312:
A subtype applied only to outsiders. [...] Creatures with this subtype are native to the Material Plane [...]
Normal tieflings fall in the latter category, they are Outsiders native to the Material Plane, that's why they have the Native subtype.
But a dark tiefling (that is, one with the Dark Creature template from the Tome of Magic p.158) is different.
Tome of Magic, about Dark Creatures, p.158:
Other creatures native to the Plane of Shadow exist [...].
Tome of Magic, about creating Dark Creatures, p.161:
[...] Dark creatures encountered away from the Plane of Shadow have the extraplanar subtype.
Extraplanar subtype, Monster Manual p.309:
A subtype applied to any creature when it is on a plane other than its native plane. [...]
From these quotes it's clear that Dark Creatures are native to the Plane of Shadow, unless some other template or effect applied later changes that.
Therefore, applying the Dark Creature template to a Tiefling must mean that it loses the Native subtype, because being native to the Plane of Shadow and having the Native subtype is not possible.
Ergo, dark tieflings don't need to eat or sleep since they're normal outsiders.