i've been in the field with tons of leather products, water proofing is a misnomer of sorts. I spend hours water proofing my boots for two weeks of wilderness, hiking , hunting and such, but i also realize i have to maintain that water proofing for it to last and also cant use my boots without taking that protection into consideration. I don't just wade through any water holes i see i walk around them. Any of them will water proof your leather for a while but not for ever. Think about leather boots for a bit. Any of the water proofing s for boots will work on any of your veg tan products just the same as it will on your boots. You do know that if you walk in water all day your boots will be wet completely through. You also know if you step in one little puddle on the way to work your waterproof boots will stay dry. At some point in between the puddle and the lake the proofing will fail right. What ever you apply to your leather will take a certain amount of abuse before it needs re applied. As for veg tan leather it softens naturally as it gets used also and as the liquors used to soften it equalize. If these liquors/fats gets washed out your leather will harden back out then fail you as the fibers will start to fray, the dry cracks in your boots, and separate! Many of the leather conditioners have waxes of various kinds and can be used , remember the oils under the finish are what are keeping your leather soft and supple.
I guess if you are thinking you can make a leather collar maintenance free for you customers it aint gonna happen. lol. Offer care and cleaning instructions as well as what you recommend or have used on them. I know alot of folks don't expect to have to maintain their leather but they do have to maintain the finishes that protect the leather.