I have not tried the older versions. They are likely running under Rosetta and some things probably will not work. LV 8.20 is the first version offficially supported on Mactel and even that is not fully compatible. I have run it and not seen any problems, but I have not done anything using hardware intensively. I have run the USB-6009 without any difficulties.
I think I recall some issues with the search for examples on other systems, so your problem may not be simply a LV/Mactel isssue.
Lynn