Kennedy I agree with. Why do you think Roberts will? (Not saying you are wrong, just wondering.)
I think as conservative as Roberts is he understands and worries about how the court will be perceived in the future. I also think he is smart enough to understand that the recognition of same sex marriage is inevitable and will not want his court to be seen as a road block that was passed at some point.
That does not mean I think Roberts will vote strike down DOMA in a way that makes gay marriage legal everywhere. I would think he will strike down the law in a way that simply forces the federal government to accept the states definition of marriage.