Relevant rules for simulacrum:
The duplicate is a creature, partially real and formed from ice or snow, and it can take actions and otherwise be affected as a normal creature.
If the simulacrum is damaged, you can repair it in an alchemical laboratory, using rare herbs and minerals worth 100 gp per hit point it regains. The simulacrum lasts until it drops to 0 hit points, at which point it reverts to snow and melts instantly.
This seems pretty cut and dry. The spell produces a "real" creature that can otherwise "be affected as a normal creature."
Still, the rules about repairing it have me second guessing whether it can be affected by healing magic. Is there any reason to believe that it cannot be healed by healing magic?* Is it safe to assume that the ability to repair the simulacrum exists parallel to healing magic, allowing characters without healing magic to repair a simulacrum?
*Perhaps a monster entry, DMG information, or developer word-of-god.