I found that Crazy Crow's German tan hide takes well to walnut dye, stiffens a little and needs some re-soffening and loses it's soft feel but seems 'tougher' when fully dry.
But I found stuff like Montana Pine Pitch made it almost 'gooy' untill fully dry, also I personally was not pleased with the color it turned.
Best bet is to obtain a scrap piece of any leather/hide and Test what you want to use before applying to a finished product.
Also keep in mind that Crazy Crow's German Tan is sueded on both sides; Sueded leather does not always take well to stuff that softens as you no longer have the epidermis (?? Skin/hair) side.
Actually some leather care products say right on them "Not suitable for sueded"
Other then then that: I used their German Smoked hide for a rifle bag and it has heald up great about four years now, weathered fine, and has many more years to go. The extra that i walnut dyed has made a pair of short legging and small belt bag - the hide gets 'more dense' after dying.
Note: the rifle bag (not case/sleeve), I mean 'bullet bag', possible bag (not really), shot bag....
It is Not treated with anything..