In 5e, succubi and incubi are neither demons nor devils, they are Neutral Evil fiends with shapeshifting ability.

What Gale is wrong at, is that RAW Cambion is any humanoid creature that was half-fiend, so they should not be limited by incubus or succubus heritage. But that appears to be a Larian's homebrew, as both Mizora and Raphael seem to be shapeshifters.