OK, you bring up a very good point. If the eggs fail to hatch because they are never fertilized, then the mosquitoes are not acting as a vector because they do not transmit the disease. I didn't even consider that possibility.

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.