The limit you are seeing is only during the initial configuration of the appliance. Once the appliance is configured, you can create as many VM networks as vSphere will allow you.  As per [URL] (page 5), there is a supported limit of 512 portgroups per VSS (legacy virtual switch).
Client says: "I am looking at the pre-configuration check sheet and it states that the Vspex only supports 5 network vLAN’s for the VMs Network.   Is this a “hard” configuration limit or just a best practice?   We have several places that have 6 to 8 vLAN’s and most have 6 to 7.  We could configure the network to operate within the 5 if we must but would hope to be able to expand it out to the 6 or 7.    Let me know if this is a hard limit so we know how to design."  Any guidance?  Thanks, Eric Marzock
VSPEX Blue VLANs