A paper on integrating VoltDB and Hadoop. From what I read, for now it works on a single direction (exporting data from VoltDB to Hadoop):
It is possible to design and develop a complete business solution utilizing both VoltDB and Hadoop from scratch. But you do not need to. VoltDB simplifies the process by providing an export facility that lets you automatically archive selected data from the VoltDB database. And you can use this export functionality with Hadoop.
See the paper below: