The DS4700 is a current SAN, the fact that it is shown as unsupported most likely means that it has not yet been ratified.
check with your vendor to see if they are going to do so.
Remember if you do install 5.1 running against this SAN you will not be in a supported configuration. if this is production you will be running at risk. I would suggest that you run this through your local VMware Office or IBM to ratify that they will support you if there are issues.