A rep for the organization tells us, "While Heidi and Spencer did not officially participate in the Avon Walk and were not there in any official capacity, we do appreciate their support of the cause and the event."
Avon also notes that Fergie from the Black Eyed Peas was the official Special Ambassador for the event.
Sources at the race tell us Heidi and Spencer did not walk the course ... but merely showed up for a short while, took photos -- and then left.
As for the couple -- Spencer's rep tells us, "Having lost a mutual friend to Breast Cancer, neither Heidi or Spencer would've missed the event. It's a cause they both care deeply about."
So far, it's unclear if Speidi donated or raised money for the cause.
UPDATE: Sooo ... Spencer contacted us with more details. He claims he and Heidi, "Accidentally happened upon the event, and immediately asked how we could participate. We would've loved to walk, but unfortunately Heidi's surgeries prevented that." Instead, Spencer says they bought "gear" to donate to the cause.
Spencer also corrected his rep's statement -- saying it's not a friend who had breast cancer ... he says, "My nana is in the hospital battling cancer right now -- so it's a cause that's extremely personal to me." Spencer says it's offensive for anyone to suggest this was just a "photo opportunity."