Dorico sounds - a duplicate of the Halion SE cubase library?

The Dorico sound library is >10GB, and I haven’t downloaded it yet. I’ve already got Cubase 12 Pro installed, with Halion SE. Are the Dorico sounds in addition to those? If I download them, will they be useable in Cubase?

Dorico does include the HSSE factory library, yes, but it also contains the HALion Symphonic Orchestra library, which constitutes the majority of the 10GB download size. You can indeed use these sounds in Cubase as well, provided you have your Dorico 4 license activated on that computer.