This is absolutely possible. You will have to do a brownfield installation of VSA and manually configure the networking, but it's easily done.
When configuring the networking, put the vswitch with the VSA-VMotion VMKernel ports on each host in the same subnet you're going to use for the back-end traffic. If you use the default 192.168.0.x subnet, give the ports IP addresses like 192.168.0.100 and 192.168.0.200, and when you run the VSA installer, use the defaults of 192.168.0.1 and 192.168.0.2.