Yes, there is hammer and filersio, but I definitely wouldn't recommend using either one. Totally unsupported, and there's no real way to controlling them properly.
I'd go for the 3rd party apps to be honest, and I'd try make it as realistic to your planned environment as possible. If you're going to be running SQL and Exchange, try running some stress tools from them also.
However the performance of the NetApp systems is pretty well known. A better way of sizing it would probably to understand fully what you are pushing at the moment and work from there. If you have access (or are working with NetApp or a Partner), then check out the customer application sizing tool where you can build up the IOPS and other system requirements.