Vladimir's Sanguine Pool description is,
Vladimir sinks into a pool of blood becoming untargetable for 2 seconds
There's detailed documentation for the abilities and effects that Vlad is unaffected by when in Sanguine Pool, such as
Will of the Ancients will not affect Vladimir even if he is the holder of the item. This means Vladimir will not benefit from the spell vamp and bonus ability power of the aura while in Sanguine Pool.