Yes, LabVIEW 6i works on the 2.4 kernel.
I am currently runing the Debian testing distribution with the 2.6 kernel and was able to at least run LabVIEW 6i. Don't use 2.6 though, IIRC there are some new threading issues that affect LabVIEW 7.0 and earlier with the new threads in 2.6.
As far as I know, there was nothing done between the 2.2 and 2.4 kernel that affects LabVIEW.
If you run 2.4, you should be okay with LabVIEW 6i.
-Duffey