No. If the Pokemon holding the given item does not defeat the Pokemon, it does not get the boost.
As for using a Pokemon with an EV booster and putting an Exp. Share on a Pokemon, if the Pokemon with the EV booster defeats the opposing Pokemon, it gets the boost, while the Exp. Share holder gets whatever it would normally get.
Without the Pokemon holding an EV booster, a Pokemon with an Exp. Share will still get whatever it would normally get.
To Summarize - Exp. Share training is just like training a regular Pokemon, no held items or anything, in battle, other than the fact that it's not doing the battling. The EV boost holder must be the one to defeat the opposing Pokemon.
Is that what you mean? That's certainly what I pulled out of it.