(all I'm talking about is Lobster's Assumption that 2 characters can't be played by the Same Actor, I don't care about 4kids Kuro at all, it's in the past, it doesn't matter)
No Lobster, which character it happens with doesn't matter.
The Fact is, we have 3 characters played By Kazuki Yao, and 2 played by Bin Shimada
Junko Noda played both Tashigi and Young Franky
Kenichi Ono played both Dalton and Gin
Masaya Takatsuka is, Doflamingo, Gedatsu, Jyabura, AND Johnny
Toshiyuki Morikawa is Hatchi and Enel
Yasuhiro Takato is Satori (and all the Things that sounded like him) and Wanze
Aruno Tahara is Ben Beckham and Mashira
Daisuke Gouri is Dorry and Rockstar
Hiroaki Hirata is Sanji and Carue
Keiichi Sonobe is, Igaram, Baskerville, Captain McKinley, AND the leader of the Gorosei
Tetsu Inada is Brogy, Jesus Burgess, Mr. 1, Patty, AND Purin Purin
It's NOT uncommon to reuse Voice Actors, Japan does it all the time, and Jango and Franky Sound EXACTLY the same!! They even have the Exact same Introductory song!