After some searching I found that the VRA Ontology is embedded as RDFa directly in the specification’s markup. Using W3C’s RDFa 1.1 Distiller I converted the RDFa to Turtle, which Omeka will import.
Distill it yourself using:
URI: http://purl.org/vra/
Output Format: Turtle
[the rest default]
Save the result and import the file into Omeka S using:
Vocbulary file: [select your file]
File format: Turtle
Prefix: vra
Namespace URI: http://purl.org/vra/
Label: VRA Ontology
After import I see 23 classes and 140 properties. I make no guarantees about the completeness or accuracy of the vocabulary, but it’s the closest thing to an importable RDF serialization of VRA I can find.