Logically, I'd expect it to work better to have an eyelash/eyebrow tint *before* a spray tan.
And that's on account of the fact that the lash/brow tint contains hydrogen peroxide (which can have a bleaching effect) and you'd be applying product to skin that has just had the tan applied to it (and probably hasn't had enough time to "take" on the skin yet). Also when the tint gets washed off at the end, it may take some of the tan with it too...
But that's just from logic rather than experience so don't take my word for it!