Funny you should ask that. I’ve just been revisiting the steps needed to generate a Cesium terrain dataset, and varying resolution is something I may be doing a bit.
Off the top of my head, the answer is “sort of, but not quite how you’re asking”. As far as I know, you can only have a single Cesium terrain provider set at a time, so Cesium will only display the contents of a single terrain dataset. However, because Cesium terrain is a TMS tile pyramid, it’s entirely reasonable to have varying levels of detail within that dataset. So, you might have zoom level 6 for the entire world, but one specific area might go down to zoom level 10 or 11. If you zoom in on that particular area, Cesium would try to request the higher levels of detail.