Yes, Use Cases are good for Requirements. My understanding is that Use Cases are not UML artifacts, that they pre-date UML by some time. Its just that they both got popular about the same time and they were used together. My earlier comment about developers saying I should not use UML, I should clarify that they did not include Use Cases in their 'ban', so Use Cases and Data/Concept Models is what I used for Requirements and provided those to the developers for design and build activities.
A parallel issue to this is the position that some people hold that Class Diagrams and ER Data Models are equivalent; you can probably guess that I don't agree, anyone want to know why?
Dave W