Is there a way I can still use OHS to IDCS or I need to use OHS- CLoudgate-IDCS ?
From some of the resources that I have looked up it seems this is not exactly necessary but is going to be the OOTB integration mechanism going forward . There are not many details available which specifies if OHS should use CloudGate to connect to IDCS .
Couple of articles that gives details on how to achieve the integration b/w on-premise application to IDCS are here :
IDCS - How To Protect A Web Application Hosted With Apache HTTP Server 2.x (Doc ID 2364938.1)
The first article gives details on setting up an on-premise Apache server to redirect requests for IDCS to authenticate which I believe would be same in the case of OHS .
Hope this helps.