You can't use the Vitalist feature this way
There are several key points to keep in mind with the Vitalist collective healing. The first one is its trigger :
Whenever a willing member of the vitalist’s collective could regain lost hit points or ability damage, the vitalist may choose to redirect any or all of that healing to one or more other willing members of the collective as a free action.
Therefore if the situation involves negative energy targeting a living creature, the living creature will suffer the damages and cannot satisfy the triggering condition.
You can then wonder about the opposite situation, if you want to transfer to a living creature the heal coming from negative energy applied to a an undead. It won't work too because of the second key point :
The type of healing (positive energy, negative energy, construct repair, etc.) is unchanged from the original source for determining who or what can be healed.
As stated, to be an eligible target, the target of the heal transfer must be able to be healed by the source in normal circumstances. If you really want to try to benefit from this kind of situations however, some items exist, as the Amulet of Channeled Life, to solve this issue.
Note that if this rule prevent the standard heal transfers with positive/negative energy, some other heals can be common to both living and undeads and then be eligible for this feature, as the Fast Healing.