Is there any problem with using the 2002 sodium filled and slightly longer valves in a 2001 LS6 head?

 

Only the exhaust valve is sodium filled. It is done for heat transfer of the hot exhaust and the valve stays cooler in the hot exhaust gas stream. There should be no reason you can't put those valves in the head. I don't know if the stems are the same diameter, but you might want to change the seals too. I would put at least a set of yellow stripe springs in because the longer stems will give you less seat pressure. Not much, but why take chances?
The slightly longer valves are to accomodate the smaller 02 LS6 cam base circle. I don't think the difference will be a factor in your rocker geometry, 01 LS6 base circle to 02 LS6 base circle. The lifters are designed to absorb about .030 of lash. If you want Comp makes a 7.375" pushrod, or you could measure the lash and get custom length pushrods, but it seems like too much work for something that shouldn't be an issue. I just wanted you to be aware of the valve train differences.