NI-VISA can be used with many instruments, including non-NI instruments. You need a physical interface (GPIB, RS232, LAN) and an understanding of the command set the instrument understands. This is often where people run into trouble, using NI-VISA with non-NI USB-GPIB or USB-serial converters.
NI hosts instrument drivers for LabVIEW (usually written by the instrument manufacturer) here - https://www.ni.com/en/support/downloads/instrument-drivers.html
Sometimes you can also get drivers written in LabVIEW directly from the vendor. You can use these drivers in LabVIEW to write your own code. Here's how to get started with those drivers- https://knowledge.ni.com/KnowledgeArticleDetails?id=kA03q000000x3XpCAI&l=en-US
If you provide specifics (instrument model, driver type, etc..) you will likely get more specific help.
Craig
