I believe the correct answer is, only when it's oxidized. Raising the chlorine will oxidize the iron and cause it to be able to be filtered with poly. If precipitated, poly will not filter much. I'll let the experts correct me if I'm wrong, but I'm fighting the same issue...
If you have iron in your fill water then polyfill will capture the iron.
If you lift stains in your pool using an Ascorbic_Acid_Treatment then polyfill will help capture the iron so it does not redeposit ont he pool surface. A sequeterant will also capture the iron but not remove it from the water the way polyfill can.
The best time to use polyfil for filtering iron is after you added chlorine and the water turns green.
If you are like me and have occasional iron issues. I just realized this year my liner was stained
by iron. Gonna try jack's magic next opening to hopefully get rid of them.