If the drivers are pure G (LabVIEW) then they should work under Unix, with the possible exception of bit-swapping(different bit order?), ActiveX, System calls and so on. "Normal" LAbVIEW calls should work on both platforms.
If the Driver calls DLLs, they won't work.
There are also some differences in how Windows and Unix machines respond to some File I/O VIs.
It's hard to say without having the code to look at (I don't know if Keithley's drivers are open or not, so it's maybe best not to post).
Shane.
Using LV 6.1 and 8.2.1 on W2k (SP4) and WXP (SP2)