Sure. Replace the certificate and private key of WebADM's web server by yours. They're /opt/webadm/pki/httpd.crt and /opt/webadm/pki/httpd.key. Then restart the webadm service.
I think windows uses the .cer extension for its X.509 certificates, but the format of the files are the same.
If you input the right information at WebADM's setup, you can re-use /opt/webadm/pki/httpd.csr to just generate a new http.crt.