Two possible workflows that come to mind:
1: You could try creating an interference check in Revit between air terminals and ceiling and then parse that information to get the ceiling information. https://forum.dynamobim.com/t/interferencecheck-parse-recover-the-elements-of-the-linked-file/9376/5
2: Do an intersection check in Dynamo of the 2 categories(with element.geometry or element.boundingbox) and work from there