By lost I mean legit DLC that is no longer available for purchase.  (In this case, the Spinal Tap pack). I was hoping to get this.. Is it ok to upload those songs into the DB?

No, it's not okay, our rules clearly states that.

Very weird rule considering what's available and the main function of the site, just imho some hypocritical nonsense.

Someone charges for a pack, than removes availability to download than its off-limits?

I feel you OP and came here searching what the deal with the silly rule is, desperately trying to get a pack I lost and of course can't download from here because "the rule"

Something needs to change or be adjusted with this "rule" ... Prime example would be a freshly charted version - should be allowed at a minimum.

If you purchased the DLC then you can still use and download it. All oDLC purchased still shows on your Steam account and will be redownloaded whenever you verify the game files or install the game. 

The rules are the way they are for a reason and they are not up for debate. If there comes a time when there are changes we will let the community know.