I never had an issue downloading from their website before until now myself. And, when I did ask them directly, they indicated that I needed a contract.
I have a small Mellanox SAN for an ESXi lab. I've been running ESXi 5.1 on it, so I decided to experiment with 5.5 and 6.0 to get experience. When I went to the drivers at http://www.mellanox.com/page/products_dyn?product_family=36 it said:
So, I contacted support, and got this reply...