Like you stated, it is going to depend on what's in the program.
LabVIEW 6.0.x didn't have the Event Structure, so if you used that at all, it will not convert correctly to 6.0.x. I think it tries to insert a Case Structure where it sees an Event Structure. Also, there are many property node attributes in 7 that are not in 6, so that may be another area of concern.
Another thing, you can't save directly to version 6.0.x from 7, you have to do it steps. First you save to 6.1, then open it in 6.1 and save to 6.
I'm sure there are other things that will cause it not to work, but the only way to know for sure is to just try it and see what happens.
Ed

Ed Dickens - Certified LabVIEW Architect
Lockheed Martin Space
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.