They certainly procreate among each other. The question is whether they procreate with the non-altered species. What they say in the article is that there was a positive correlation between isolating mating behavior and the different alleles used. In other words, they still mated, but less so. When that is combined with adaptation to different environments, mating might be less.
We already know that closely related species in the same environment, like Darwin's finches, do mate but at reduced frequency.