Who are the models in these two campaigns?

Yes, they are the same. She's Catherine McNeil, an Australian top model which is in high-demand right now. She first appeared on the fall 07/08 runways, which caught the attention of influential photographer Mario Testino. Testino immediately signed her for an exclusive 6-month contract, meaning that no other photographer can use her during that period of time. Both the campaigns you mentioned (Donna Karan and Hugo Boss) are shot by Testino. During those six months, she was also shot by him for the covers of V Magazine (#47) and June/July '07 Paris Vogue. The fall 07/08 Versace campaign also featured her with Kate Moss, and it is also shot by Testino.