I really like Roxas' voice but that is only because I heard him talk the first time I saw him. If I had been looking up spoilers before KH2 (I wasn't a massive fan back then so I didn't) and saw Roxas then maybe I would have imagined a different voice for him like with all the CoM organization people (apart from Axel) because I had been looking at pics of them for a while without seeing videos with their voices. Because of this is could have been disappointed with Jesse like I was with Larxene.
But it is not about what I like, if the whole point is that Roxas and Ven sound the same then it should be like that. I haven't played Days yet cause it isn't out in Australia yet but I read that Kairi and Xion have the same voice in that game so regardless of who voiced Kairi in other games, in that game they kept the japanese thing of having the same VA, I don't see why they won't with Roxas and Ven.