We hear this debate all the time… people either can or cannot be strong at both visual and UX design. My personal opinion on the situation is that someone can be strong at both, but that having one person play both roles on the same project is not the ideal situation. 
Several months ago I came across an article on UX Booth about Decoupling Usability and Visuals and I couldn’t help but see how the author’s point of view relates to this debate.
In the article, the author talks about pulling apart the visuals from the usability in order to exploit the strengths and weaknesses of both. I would agree, and I would argue that pulling them apart is much easier and efficient when there are two different people representing each role. This pulling apart is a huge part of making a design, and further, a product or site successful for the user. When that pulling apart is done by the same person, one would assume that biases towards one or the other would appear, and the solution would be weighted one way or the other… either towards the visuals or towards the usability.
By having separate minds pull apart these two intersecting points, a more pure and holistic solution can be found. A balanced compromise can actually be achieved, one that will end up being better for the user.
So, give the article above a read and let me know what you think. Whether you are someone that agrees or disagrees or even if you’ve found further research on this point. I’d love to hear more from you!