Rules and regulations: Do not add plagiarized characters, voice banks sourced from commercial artists and voice banks sourced without permission of the voice donor/source. UTAU usage policy also forbids voice banks taken from another brand of voice synthesis software without permission. (The only exceptions to this rule are Macne Families, FL-chan and Iku Acme; Voice sources/software/plugins deemed royalty-free are allowed.)
Gagapoid's existence is illegal but as long as someone does not distribute the bank, Ameya won't get into too much trouble. But I still think making a voice bank without consent of the voicer wouldn't be good idea.