Plants don't care what they grow up on. They don't know the difference between a tree, a fence, and a teepee. Of course, if the tendrils don't have anything to wrap themselves around, they simply won't climb. Also, most anything growing at the base of a tree, in the same soil, is going to be competing for water and nutrients with the tree roots, and sitting in the shade of said tree, neither of which is going to be good for cucumbers.
