No! They just kissed in an attempt to win a challenge. On further investigation, one might think that Duncan likes Heather, due to him accepting Heather's cuddle in both Are We There Yeti? and Master of Disaster. However, he is probably just doing this to annoy her. He also finds her attractive in the first episode of TDI:
Duncan (passing by Heather at the dock): Meet you by the campfire, gorgeous! Heather (offended): Drop dead, you skeeze! However, he uses these terms of endearment on all girls, i.e. LeShawna, Gwen, Courtney, etc. So, no, Duncan does not like Heather, only does it for kicks.