The official framework describes the applicant making a gift after vetting; it does not describe a financed product. Whether borrowed funds are acceptable is a question for the current official instructions and counsel, not for the broker offering the loan.
Test the financing idea against the instructions before the term sheet
The broker's pitch is that the contractor keeps his sale proceeds invested and services a loan instead, so the gift costs him interest rather than principal. The official process, as published, involves an application, a nonrefundable processing fee, vetting, then a gift to the U.S. government on instruction, and successful applicants are placed in an EB-1 or EB-2 classification subject to visa availability.
The published material addresses the gift and the fee; it does not market a financing arrangement, and an applicant who arrives with a lender in the background should expect the funds to be examined like any other. Before signing anything, ask counsel to read the current instructions and say in writing whether borrowed funds are addressed, and ask the broker to explain what security the lender takes and what happens if the application fails after the fee is paid. Eligibility for permanent residence, admissibility and visa availability remain separate requirements that no financing structure satisfies.
If the answers are vague, the contractor is being sold a loan, not a route.