Currently we have 3 examples of individuals summoning primals into themselves (I'm not including the Lucavi as they are a different beast altogether): Ysale with Shiva, Archbishop Thordan with King THordan and Yotsuyu with Tsukiyomi.

Ysale had the echo and the blessing of light, but according to Hraesvelgr, had deluded herself into thinking she was Shiva reborn instead of manifesting her vison of Shiva.

Archbishop Thordan, so far as we know did not have the echo, yet summoned Thordan within himself, seemingly multiple times to temper the Heaven's Ward. Despite this no one noticed anything out of the ordinary with him. While the Heaven's Ward could be excused as they were only lightly tempered, calling a Primal into oneself seems like it would do more than lightly singe one's nature.

Much the same could be said of Yotsuyu. She summoned Tsukuyomi into herself with a few chests of crystals and a hand mirror. Like Thordan she seemed to not have the echo. Although there is something Tsukuyomi did that no other primal has done: Draw strength not from faith or crystals, but from her summoners memories of suffering. Since a part of tempering is the dampening of a sense of self it seems peculiar that a primal can draw from something that requires a strong sense of self.

Of course it could also be that becoming a primal even once without the echo changes one to a point where the question of tempering is meaningless. I mean Ifrit can temper, does that mean he is tempered to himself?