dctype:Dataset is part of the DCMI Type Vocabulary, alongside text, image, sound, software and some other genre terms.

In DCAT 1.0 dcat:Dataset is a subclass of dctype:Dataset. However, the scope of DCAT 'dataset' is more general than the DCMI Type 'dataset' (see Scope or type of dataset with a DCAT description [ID8]), and also includes 'text' at least, and maybe multimedia types as well - the Datacite-DC-DCAT mapping provided at #64 (comment) certainly shows this.

So, while the DCMI Type Vocabulary could reasonably used as a typing vocabulary for classifying a dcat:Dataset (see #64), it is incorrect to pre-empt this by making dcat:Dataset a subclass of dctype:Dataset.