While the underlying concepts are similar I guess the issue would be does the Fusion-IO card in a Vblock configuration support the same functionality? The main functional difference I am thinking of is that as I understand it the EMC solution uses their card for reads and writes through it to the underlying block storage so that in the event of a failure that the data is stored and protected externally to the host and the card. If Fusion-IO supports this then either solution would be fine but if not then it comes back to the potential limitation of having your data on a PCI card inside a server that could fail at some point.
I suspect the reason EMC calls it VFcache is that is a good description of what it is doing.
The Fusion-IO products work well but I find the overall solution set from EMC to be compelling.