Nothing to debate with the Dojutsu's.. Camouflage detected by Obito worked by reflecting light around the user. Mu's invisibility works by having water particles reflect light around him. As shown on many occasions, light is no problem for Dojutsu seeing how it can see through dense substances and body parts, meaning light reflection is irrelevant (and was in Obito's case). Seeing how the invisibilities are practically the same, said Dojutsu spots Mu without much problem, whether he suppresses his chakra like Karin or not.