Hi,
There shouldn't be any interaction between the two GPIB drivers. The NI interfaces will use NI-488.2, wil the Keithley interfaces will use their low-level device driver. Each driver will manage the their own hardware.
In LabVIEW, you will use the NI-488.2 Vis to communicate with the NI interface. The Keithley driver has to install their own driver interface VIs.
The only problem is you want to use VISA for both interfaces. I don't know if there is a Keithley implementation of VISA, but there can nly be one installed in the system. The NI_VISA driver will allow you to control the NI interface, but not the Keithley interface. You can still use the Keithley interface using the low-level driver.
Finally, here is a knowledge base I found that has
some information that may be useful to you
Using a Keithley PC488 GPIB Interface with LabVIEWHope this helps.
DiegoF
National Instruments.