In Warcraft III: The Frozen Throne, voidwalkers were portrayed as slender creatures. In World of Warcraft, they are much bulkier. Voidwraiths may be the type seen in The Frozen Throne or be inspired by this incarnation.
Creatures like Vexallus, Anomalus, and Arcanimus are elemental creatures that have a similar body shape to voidwraiths. They are sometimes called "arcane voidwraiths" (their model name) by fans for this reason, but there is no indication that they have any affiliation with the Void. More likely they are arcane elementals or possibly a type of mana surge.