AA tells me that the carry-on limitations on American Eagle are the same as for AA in general, and that the aisle is just as wide for roller bags. Does anybody know if this is accurate?

The aisles on the American Eagle planes certainly do not feel as wide as on the larger jets! The overhead bins are much smaller and roller suitcases that will fit in the larger overhead bins on the large planes are checked planeside and picked up at the bottom of the steps when you land. We have even been giving over our large backpack planeside before boarding in SJ for Bonaire as it is a tight squeeze on the Eagles. Security of bags checked plane side is not an issue as you hand it over, it goes into cargo and you pick it up plane side.

If you are referring to the ATRs flown SJ-BON-SJ, small carryons go in racks overhead the seats. Larger ones are taken at the cabin stairs and fly in the forward cargo area. They are returned as you disembark. I suspect a carryon large enough to use its wheels in the short aisle will be put up front, making aisle width moot.