Reap the Damned (Assemble Abomination) states “If a wraith is consumed…” Blood Spectre (Sacrifice) states “When you sacrifice a minion you have a chance to assemble a Blood Spectre…”
The effects of Reap the Damned also apply if the consumed minion is a blood spectre rather than a wraith, which is unexpected.
(My personal 2 cents is that this is a cool interaction, but it could use some tooltip/name clarification)