Question: Do I need install DX Gateway to integrate CASDM with DX OI?
DX SaaS
On Prem DX Gateway
On Prem CASDM
Documentation
DX OI SaaS and DX OI On Prem version 23.1 onwards, CASDM is supported out of the box (Without DX gateway).
You should see an option in dropdown menu of 'Ticket Management Type'