If it's antifreeze, it should be readily soluble in water...quick and dirty check. dip a finger into it, then into water, if it dissolves -answer right there. Motor oil will be an oily slick (immiscible in water). If it's sticky, I'd be willing to bet that it's the ethylene glycol residue from antifreeze after the water has evaporated...headgasket, almost certainly. Those twonks at the dealership should be held completely accountable. Good luck and keep us posted.
Jim
aka, VeloXXiraptor