That comes perilously close to a “strawman” argument. I won’t speak for anyone else, but I have no dog in this fight since I’m not even Catholic. See, I think this Christian Aid Mission uses the “we’re only trying to save nominal Catholics” angle as just that, an angle.
However, the situations discussed in these “success stories” on the Christian Aid Mission website, strike me as not much different than the stuff Catholic-bashing is made of in the US, that Catholics are “unaware of salvation by faith” and “don’t really know Jesus”, don’t read the Bible, see saints as deities and engage in idol worship.
I’d have given the CAM the benefit of the doubt, except for this “testimonial” from Spain, in which they state as fact that Holy Week in Jerez includes “processions with idols”.
Last I checked, Spain is not a hotbed of syncretism. This convert was not continuing in native pagan traditions but simply changing the pagan deity names to saint names. Indeed, this is the description of processions in Holy Week in Jerez from a more neutral source:
catavino.net/the-pointy-hat-brigade-holy-week-in-southern-spain/
Apparently, to the CAM folks, the Virgin Mary is an idol. They completely show their hand here, describing a centuries-old Catholic tradition in an European country as “processions with idols that evangelicals eschew”. Note how they themselves focus on the differences between Catholics and evangelicals.
No, they’re not just reaching out to the lost sheep that are the victims of poor catechesis and evangelical activity by the Church. They’re also looking for the sheep already in the fold. Or, as the OP states, sheep-stealing.