So it's safe to say that they're friends, while Nancy and Vicki are not, based on their Twitter conversations posted below.
You can read on these tweets that Nancy hasn't met Dra. Vicki Belo yet nor been introduced to each other.
(In Dec. 16, 2010: Nancy described Dra. Vicki Belo as hot when she saw her at Greenbelt 5.)
(Nov. 29, 2011: Nancy & Hayden talkin' about Hayden Fragrances.)
(Dec. 22: Hayden offered help to teach Nancy's twins, Matteo & Joaquin, how to eat "lugaw" using chopsticks.)
(Dec. 22, 2011: Nancy asking Hayden, DJ Mo Twister, Zoren Legaspi & a few others when they're going to meet up for a drink)
(Jan. 10, 2012: Hayden asked for Nancy's number, which she sent via DM or Direct Message)
(Jan. 10, 2012: Hayden Kho wanting to introduce Nancy Castiglione to Dra. Vicki Belo)
(Jan. 23, 2012: Hayden reacts on Nancy's tweet about wanting to eat fried "tikoy" and wanting to see Edward Norton, who was reported then to have arrived in the Philippines to shoot for "Bourne Legacy".)
(Feb. 9, 2012: Hayden comments on a photo of Nancy and her twins)