Are all datasets in Data Catalog "Open" and freely shareable?

No. Depending on the license and restrictions with the data providers. Some datasets may have restricted access.

Who owns the datasets listed in the catalog?

Not all datasets in the catalog are owned by SDI. Neither of the responsible or point of contact of the resource. Data ownership and terms of use are determined by agreements between the parties responsible for creating and maintaining the dataset. Data ownership is an important consideration in the catalog, and is reflected in each dataset's metadata.