I really don't think it will hurt. That said, I don't really think you need to raise the temp to dry hop. I do it cold all the time while cold crashing, before cold crashing, after cold crashing, in the fermenter, in the keg... you see what I'm getting at? Until I'm convinced it has a measurable difference in the final taste of the beer, I would just do what is convenient for your schedule. By warning it up, all I would see is then having to cool it down again to carb and drink it.