He was telling you something real, though it's two separate points and only one of them is a problem.
The depreciation point is straightforward. A syndication passes depreciation through to its partners on a K-1, and that paper loss offsets taxable income. An IRA doesn't pay tax on its income in the first place, so there's nothing for the loss to offset. It isn't destroyed, it just does no work. What the IRA gives you instead is that the whole gain at sale grows without current tax, which is a different benefit rather than a smaller one. Which trade is better depends on your own tax picture, and that's a question for a CPA.
The second point is the one to take seriously. When a tax-exempt account earns income from a business or from property bought with borrowed money, a portion of that income can be taxable to the account itself. Syndications almost always carry a mortgage, so the debt-financed portion is the relevant piece. It's often modest during the hold and larger in the year of sale. The rules here are specific and the account may need its own tax return filed by the custodian at your expense, so confirm the mechanics with a tax professional before you wire.
Two practical things about the custodian. Their fees are ongoing, commonly a few hundred dollars a year plus a per-asset holding fee, and some charge per transaction, so ask for the whole schedule in writing. And every dollar the deal distributes has to go back to the IRA, not to your checking account, and you can't personally guarantee anything or do work for the property. Those rules on self-dealing are strict and the penalty for breaking them can reach the whole account.
