Hi,
with OpenVAS/GVM 9 OMP got renamed to GMP (Greenbone Management Protocol). GMP is the protocol for requesting data from the gvmd daemon. See https://gvm-tools.readthedocs.io/en/latest/glossary.html for some details about the abbreviations.
Of course you can also speak with the scanner directly. This depends on the used version of GVM. With GVM 10 and below the scanner daemon is called openvassd and uses OTP. With GVM 11 we switched to a Python based daemon implementation called ospd-openvas which uses the XML based OSP.
By default both scanner daemons are listening on unix sockets. The socket location always depends on your installation method.