It appears that, as usual, with View and vSphere having separate release times, vSphere 5.1 will be incompatible with the current version of View. According to the document at http://www.vmware.com/files/pdf/techpaper/Whats-New-VMware-vSphere-51-Performance-Technical-Whitepap..., "NOTE: vGPU support is enabled in vSphere 5.1, but the ability to leverage this feature is dependent on a future release of View. Refer to the View documentation for information on when these features will be available.". I've looked at the View documentation but don't see where it mentions what version will be compatible with vSphere 5.1. Anyone have any insight or information that they can share?
Unfortunately I can't say much since there are still factors that may cause this statement to change but there is a possibility that a release in the 5.1.x line will contain support for vSphere 5.1. I'm not sure if this will enable the vGPU features or not but I would check the release notes of any other 5.1.x releases that come out. (This feature is not in the 5.1.1 release).
Support for vSphere 5.1 will definitely be in the next major release of View though.