Not fully, but quite close to fully.
Celcom support USSD over IMS (u can dial *118# on 4G+ without dropping to 2G) and most Celcom MVNOs are still under default Celcom routing.

There's still a plenty number of sites that are still not integrated. Nevertheless, day to day use u probably will not feel any differences now since Celcom joined the Digi ASN4818, unless u are ''lucky'' staying in the place where the network has not been integrated