You can say the same for Tour de France too... if Sky is serious about winning the Tour with Froome I think they will need to send one of the Colombians along with Porte. So I can definitely see the Colobians being split for Giro and Tour, I just think it makes more sense for the designated leader for the Vuelta to do the Giro.
However, I think it's possible for Henao to support Froome in the tour and then lead the Vuelta. Unlike Froome last year, Henao will not be Froome's last man (that will be Porte's role), will not be competing in the ITTs, will not be leading out Cavendish on the flats, and will not be competing in the Olympics. If Henao does the tour, he will be much more fresher in the Vuelta than Froome was last year.