UniProt Consortium is publishing its data in RDF since 2008. However UniProt runs its own sparql endpoint located in Switzerland and is therefore not directly part of the RDF platform. The data is also available via ftp. For questions concerning UniProt, please use their contact form.
However, keep in mind that it’s possible to combine RDF resources via federated sparql queries!
You can find an example for federated queries between the RDF platform and UniProt on our documentation page using sparql and at our sparql endpoint.