A significant factor for the development of grey literature delivery systems was open source software and open standards capabilities and availability. Open source software powers a significant number of grey literature systems implementations, including repositories, digital libraries, etc., while the definition and provisioning of open interoperability standards allows the delivery of value added services. Open source and open standards have achieved at enabling the provision of grey literature infrastructure and technology to a wide community of professionals and the public, thus achieving a high level of interoperability and technological platforms costs reduction. However, a paradigm shift is under way, in the way content and grey literature content in particular, can be organized, aggregated and delivered. Additionally to the open source systems increasingly discussions are made for utilizing the Cloud capabilities, where under the uniform term Cloud, various technologies, business and service models are aggregated. In this paper a technology survey and assessment of the current state of the art for providing Cloud based services for Digital Repositories, Digital Preservations and repository interoperability, is made. Solutions that integrate Cloud based technologies and elements, or entirely Cloud based solutions are expected to increase in the forthcoming years. The various Cloud technology service models (Infrastructure as a Service, Platform as a Service, Software Service) and the capabilities they offer for the implementation of repositories, digital preservation and interoperability systems, are examined. In the full paper the opportunities, challenges and requirements posed by this paradigm shift are examined, especially from the point of view of Grey literature oriented Repositories and systems. The increased significance of open standards, in the light of migration among different Cloud providers, the neutrality of Cloud operators are especially targeted. Furthermore, as a specific case study, the efforts made by the National Documentation Center of Greece for providing a Repository with the Software as a Service Cloud model and an online Open Standards Validation system are presented. The Repository as a Service system builds upon previous e-infrastructures of the National Documentation center, and is provided for Greek public institutions as a SaaS based tool for organizing and delivering grey literature content, in a viable manner. In the area of interoperability the provisioning of a centrally managed Interoperability Validation tool, for validating conformance to a set of existing international open standards is presented. This validation tool is going to be used for validating interoperability features by a series of Greek digital culture projects, which can include grey literature material. This validation tool provides the necessary framework for ensuring, actively the interoperation of the various digital repositories projects, whether Cloud or standalone based, to aggregator services and for providing additional value added services.