Ryo In my interpretation, no.
You have to differentiate between Inhabitation and Possession; only Inhabitation results in True Form, Hybrid, and Flesh Form merges, Possession does not.
A Spirit using the Possession power on a Living Vessel and succeeding in its Force x 2 vs the vessel's INT+WIL results in the spirit Possessing the vessel, and the Spirit's Force is added to the vessels Physical attributes only for the duration of the Possession.
A Spirit using the Inhabitation power on a vessel (with the help of a Magician) and succeeding in it's Force x 2 vs vessels INT+WIL (after the Force x days preparation time) will always, and permanently, Inhabit the vessel as long as the Spirit doesn't roll a glitch. It'll be as a True Form, Hybrid, or Flesh Form depending on the dice roll.
Physical attributes of Inhabited vessels are only augmented in the case of hybrid forms, as per page 100 of Street Magic. Neither True Form or Flesh Form merges gain these bonuses.
In short, a Flesh Form gains Immunity To Natural Weapons (like the Hybrid), and also gains Realistic Form and Aura Masking, whereas the Hybrid gains the boost to Physical stats instead of the latter.