Kyounosuke is the voice provider for Nekomura Iroha. There is another voice synthesizer program called Alter/Ego, and one of their CVs (for ALYS) was provided by the YT singer Poucet. DEX and DAINA's voices were provided by the producers Nostraightanswer and EmpathP, and they both sing occasionally. The Chinese utaite Chalili provided the voice for Xingchen. Those are all the ones I know of, and I'll let you know if I find any more.
WINDOWS UTAU 100%. They're purchasable UTAUs mainly voiced by utaites, such as Lon (as Amaha Sora) and che:Sakurai (as Sakurai Kaon).