As a practical matter, that is true. Regional Centers do not generally accept you to file an I-526 petition before wiring the funds to the escrow. USCIS, in their website, cite as follows:

The petitioner must establish he or she meets the following eligibility requirements when filing the Immigrant Petition by Alien Investor (Form I-526): The required amount of capital has been invested or is actively in the process of being invested in the new commercial enterprise.