Traffic and Closures, even though the info comes from the same place, are treated differently. You can configure Traffic to either auto-recalculate in which case your GPX1.2 route will probably be destroyed depending on your routing or prompted and then it's your own doing. My advice would be to treat traffic warnings with suspicion anyway.
Closures still need Traffic to be enabled to be seen and acted upon but there is no option for auto/prompted - your route will be recalculated and often disastrously with Zumos older than the XT2. To clarify, even if you have Traffic as prompted, closures will recalculate your route.
It's no help to those with older Zumos but the XT2 seems to offer a more localised road closure diversion with GPX1.2. With GPX1.1, I think it depends where your shaping points are. If there is one within the closure, it may have to be skipped on your Zumo screen.