Regarding using a voice bank made in UTAU in UTAU-Synth...
It does strange things to the configurations, from what I experienced. I really don't know how to configure a bank on UTAU-Synth (all I ever do on it is test certain things because my Mac is faster than my netbook), but I know how I configured the VB I used, and the envelopes were all uniform and off. e.g. I configure my hard consonants with zero or negative overlap, and they sound really clear, but when I used the VB in UTAU-Synth, everything from hard consonants to vowel transitions appeared to have the same envelope and the consonants were all muffled and slurry as if configured incorrectly...
And yeah, there's also, Wine or using a Windows Virtual Machine and downloading UTAU for that lol.