Hi pacificbill,
According to the readme files for the Linux NI-VISA drivers, only 32-bit versions of the OS are supported. You can find the readme files by navigating to ni.com/drivers, selecting NI-VISA, and filtering for Linux drivers. Once you click on one of the versions, there will be an option to open the readme file.
In regards to your DIACAP accreditation question, I am currently asking around to see if anyone can shed some light on the question.
Regards,
BluJae