In addition to Thucydide's answer of an aggressive informational campaign, there are a few more steps this second country can use to turn their enemy's practices into their own benefit.
While they are broadcasting how abhorrent it is to hunt down and harvest unwilling people for these devices to undermine the other country's war effort, they can also offer sanctuary for any of these 'gifted' individuals who can cross the border, and also their families (who will fear for their future generations). There might be some spies, but probably very few would be willing and fewer would be successful, since they would be betraying themselves or their families to the harvesting if they succeeded - and the community would almost certainly be trying to self-police, since that kind of behavior would risk them all.
Additionally, the second country, who will have a much higher population of the inherently gifted, might be able to recruit and/or train some of these people with lesser gifts. The gifted will be more likely to come forward to defend themselves and the country that shelters them, from the harvesting country, than would come forward to be harvested. With a higher population, there will be more resources to activate latent gifts, or train unreliable ones, or discover technology that might amplify or stabilize gifts to a lesser degree, which also don't require human sacrifice. This might eventually end up with a situation where squads of gifted people work together to face off against soldiers with meta devices. As a bonus, such squads might be more flexible and adaptable than a soldier with a single device.
Next, with a strong stance against human sacrifice and for protecting the naturally gifted, it might be possible for this country to make some limited use of the meta-devices anyway. One example would be captured devices, which are known and published to be captured, being re-purposed (assuming the original soldier dies in the capturing). If done with respect to the ethical questions it raises, after consulting the population of naturally gifted, acknowledging those sacrificed to make it, and letting families of those sacrificed have some say - they can probably be used without undoing the good propaganda against their being made. Even if not, capturing them and storing or destroying them will weaken the enemy forces by quite a bit.
And, with the higher population and more protections given to the naturally gifted, there will probably be more willing to volunteer to be sacrificed if there's some meta-ability where even one or two meta-devices will make a huge difference (ie, let them grab or neutralize a lot of enemy meta-devices), and if those volunteering are very obviously willing, maybe drawn from the already terminally ill, and if there's a real perception that this kind of thing is accepted by the country reluctantly and only due to great need. It would be dangerous to the country's morality, though, and should only be done if it gives an overwhelming advantage for a very low cost.
These "gifted" will obviously prefer a country who treats them well and offers human rights and protection, over one that hunts them down and sacrifices them... and that will move such "resources" from one country to another under their own power. The more the second country treats them ethically, the more they'll be willing to give up for that country, and actively work against the first country.