I don't really know - I'm just careful when I specify what I'm buying. It's a _big_ problem to knifemakers. As chrome leather falls apart on its own after a few years (faster if damp), then the good stuff isn't.
If it's the classic greenish-grey colour of cheap rigger's gloves, that's definitely chrome tanned. When it's dyed though, I'm not sure how you'd tell. Maybe measuring the pH ? The stuff is pretty acidic.
-- Smert' spamionam