Mosquitoes are a vector that spreads disease-causing germs to a population. The proposed solution is to use different mosquitoes as different vector that spreads a different disease-causing germ to a different population.
They won't harm then it sounds like, but they'll not fertilize the eggs.
However, it turns out the eggs are fertilized. Note that the FAQ says the males are effectively sterile and links here: https://en.wikipedia.org/wiki/Cytoplasmic_incompatibility
That wikipedia article says that there are embryos, but the embryos die.
However, the real question to ask, I guess, is whether the embryo is infected. As I read that article, it sounds like it isn't. Instead, the male parent is infected and this creates sperm which can fertilize the egg but in a way that creates an embryo that can't survive. In other words, the male parent has an infectious disease which causes the embryo to have a fatal genetic disease.
So this also brings up another question: what exactly is a vector? In this scenario, the embryo has a disease it would not otherwise have gotten, if it weren't for this germ. However, the embryo doesn't have the germ itself. Is being a vector defined by whether some disease is caused, or is it defined by whether the germ is spread? I don't know.