Why hasn't Obito been ressurected yet??

[hearteaterx]

Does Kabuto's forces really need a genin to their team? A genin with one eye and half his body? Think about it

You don't see how IWR works. IF Obito were to be rezzed by Orochim-er, Kabuto- then Obito would have 2 sharingan eyes + a complete body.
On topic, Obito isn't summoned for the same reason Nawaki (Tsunade's lil bro) isn't: Kabuto isn't threatened by ninja that chunin can defeat...