I have an aircraft jacket in ventile - even thought it doesn't say it is. But when water hits it it stiffens..but eventually soaks through.
I would say ventile is shower proof at the most, from what I experience. I don't know how companies like Private VC say their ventile garments are waterproof, when I think of waterproof I think if gortex.
I would not wax the jacket, maybe you can washing and reproofing the jacket. Below is straight from ventile site: