I saw it on vmware blog Horizon view adapter for vrops but is it requires separate license or is it part of horizon view suite?
View Adapter for vROps requires two keys, both of which are included with the Horizon Enterprise license. The Horizon Enterprise license that you put in the connection server license the adapter, and an additional set of licenses licenses the manager. It's basically done this way so folks can deploy vROps for their Horizon environment, but don't own vROps for their server environment.
This article is the best description available, but it somewhat tricky to understand.