VSC still needs to be installed on a windows server for it to register to the vCenter Appliance.
My recommendation is to install it on the same server VUM is running (since VUM requires windows anyways).
Ofcourse VSC 4.2.1 isn't supported on Server 2012, so if you want to install VUM 5.5 U1 on windows 2012 r2, you're going to need to install VSC 5.0x6, but then you get web-client VSC functionality.