The only rain one needs to be concerned with is when the bike isn't running. Riding in the rain and ingesting water while the bike is running isn't going to hurt anything. The little bit of moisture that might get sucked through the filters is nothing, it would take submerging them to do any damage.
Now if the bike is sitting in the rain for long enough and not running, small amounts turn into large pools. The shape of the filters probably wouldn't allow for that even left exposed to the elements but stranger things have happened and why chance it.