Yes you can use other vendors seminar/webinar to report your CPEs. The reporting portal will guide you through the process.
You do, however, need to keep records on the attendances, in case being audited. Things like post webinar acknowledgement by the presenters, certificates of attendances, etc.
Just remember, you have signed the code of ethics, so just be honest and truthful when filling out the CPE.
Chuxing Chen, Ph.D., CISSP, PMP