Depends on the setting OP.
First of all, is there a difference between the undead and construcs beside the name ?
Because sending mindless constructs to war comes with it's own moral questions.
Most DnD setting have undead where you tear the soul out of the afterlive and basically staple it to it's old rotten body and give it an IKEA replacement for it's old mind and what you have is basically the "I have no mouth and i must scream" situation.
Instead you could use other creatures with lesser or no sentience to use them as "Ablative troops" in your setting, like domestic animals and pests.>>57642827