Starwind free I find is pretty good for whiteboxing Iscsi targets. Another popular one is Openfiler however I have not used that for a few years as I've got an old iomega ix2 that I use for NFS storage. AFAIK if you mean uberVNX I;m pretty sure its NFS only.
If you are going to build a whitebox pc to lab the entire thing (ESXi, storage, networking etc) then any box will do and use VMware workstation to build it all in. Just make sure you get as much memory as possible 16GB is good or Intels upto 32GB is better. Also get 3 different disk drives, I would get a standard 320 or similar OS drive to install windows directly onto the whitebox then install workstation on that. Then a larger disk for slow storage for vm's where performance does not matter quite so much and then a SSD (the most capacity you can afford) to put the vm's you are actively working on on. Labbing things out on sata disks soon becomes tedious when you have a handful of vm's running from it.