1. Is it at all supported (by VMware and/or NetApp) to run everything over one single vmkernel port on one single subnet? It's not listed as an alternative in http://www.netapp.com/us/library/technical-reports/tr-3749.html as far as I can see.
I assume you mean a single vmkernel port for NFS traffic? This is a common practice and is included in many vendor build guides (Vblock comes to mind as one). I'm curious what your use case is for additional NFS vmkernel ports on a single subnet, as they would sit idle.