Leaves contain tannin. So can you vegetable tan hides with leaves?
just

^^^^^
Tree bark is better, and what has been used for thousands of years. Oak being one of the common barks being used.

Probably a very thin skin like rabbit.Tea leaves contain some tannin.
Oak bark and Hemlock bark were used back in the day to veg tan high grade industrial leather.
The bark is much higher in tannin than the leaves.
Vegetable tanning heavy leather is time consuming and fairly labour intensive but the finished product is unsurpassed by mineral tans.
I use a method to veg tan fur,it is actually a combination tan since a strait vegetable tan for furs takes too long to preserve hair roots.
Combo Veg tanning will permanently stain light coloured fur.