If I own a group of related companies, can I consolidate employees across those companies to meet the criteria of a large operating company exemption from the reporting company definition?

No. The large operating company exemption requires that the entity itself employ more than 20 full-time employees in the United States and does not permit consolidation of this employee count across multiple entities. FinCEN’s Small Entity Compliance Guide includes a checklist for this exemption (see exemption #21).