After doing a few tests I can confirm that the OIDC module supports OAuth features including the ROPC grant.
I was able to use a simple curl command to test:
curl -X POST \
https://<your login server>/cas/oidc/accessToken \
-H 'Content-Type: application/x-www-form-urlencoded' \
-d "grant_type=password&client_id=<CLIENT_ID>&client_secret=<CLIENT_SECRET>&username=<USER>&password=<PASS>&scope=profile"
If you use this to test, make sure you update the values I surrounded with <> and adjust or remove the scope parameter.
You can then pass the received access_token in a post request to "https://<your login server>/cas/oidc/profile" to retrieve the claims you allowed your app to access.