ETFs trade like stocks. You should have not problem holding it in an IRA regardless of what's held in the portfolio. As an example, look at Direxion funds which are 3x the direction of the market (bull and bear.) You can hold those ETFs also in an IRA.
I have become concerned with what is held in my IRA since learning that purchasing certain assets can cause an IRA to become taxable. I own GTU which is a Canadian gold trust with shares trading on the AMEX. I'm not sure that it's a legal IRA asset since i am invested in metals that are not US coin, such as gold eagles. If you have any info on this I sure would appreciate your thoughts.