The dividing line is usually loan purpose and who the borrower is, and it's set by state law as well as federal, so the answer changes when you cross a state line.
Federal mortgage originator licensing under the SAFE Act, and the consumer protection rules in Dodd-Frank and TILA, are aimed at consumer-purpose loans secured by a dwelling the borrower occupies. A business-purpose loan to an investor buying a rental generally sits outside those rules, but the exemption turns on the loan actually being business purpose, documented as such, and the borrower not moving in. Several states then add their own licensing on top, and a few require a license for anyone making even one mortgage loan, while others have a de minimis exemption for a small number of loans per year. Whether your specific loan needs a license in your state is a question for an attorney licensed there, and it's a cheap consultation relative to the risk.
Since the lender is your IRA rather than you, get the mechanics right too. The note and the security instrument name the custodian for the benefit of your IRA, in whatever exact vesting language that custodian requires. The lender's title policy should insure the IRA as the insured lender, and the borrower's hazard policy should name the IRA as mortgagee so you get notice if it lapses.
One more: escrow and taxes. If the borrower stops paying property taxes, a tax lien can jump ahead of your position depending on the state. Either escrow for taxes or set a calendar reminder to check the county records yourself once a year.
