And just so there is no confusion on this matter.
From the Monster Manual 3.5:
"Unlike most other living creatures, an outsider does not have a dual nature--its soul and body form one unit. When an outsider is slain, no soul is set loose. Spells that restore souls to their bodies, such as raise dead, reincarnate, and resurrection, don’t work on an outsider. It takes a different magical effect, such as limited wish, wish, miracle, or true resurrection to restore it to life. An outsider with the native subtype can be raised, reincarnated, or resurrected just as other living creatures can be."
That is not canon...that is a hard, fast rule of the game.
That said, I have no problem with necromentals or lichfiends as long as they have a rational explanation, as Shemeska pointed out.