The tags could be added to the JSON-LD representation of artist and release group resources using the schema:genre property (http://schema.org/genre).
The value might be either the textual label for the tag (e.g. "pop/rock") or the URL (e.g. "https://musicbrainz.org/tag/pop%2Frock").
The latter would be preferable if a JSON-LD representation of the tag resource is available.