I'm planning on making a pasta dish tonight that uses the pasta cooking water in the sauce. Something like cacio e pepe. The pasta I've got is the high protein pasta that they make out of lentils or chickpeas. Since it's not normal pasta, will my pasta water still be usable in this way?
Yes, you should be fine. Pasta water is used to loosen a condiment, and allow it to be incorporated with the pasta during the final tossing/dressing of the pasta. The water from traditional pasta will have some starches from the pasta in it, and does sometimes help "thicken" (to a pretty small degree in my experience) a sauce, but that is not typically relied upon. If your sauce is too thin, just cook it a bit more. Too thick, add a few tablespoons of pasta water.