I doubt iron would be a problem. Lot of folks grow where soils have a high iron content, or where their well water has lots of iron. And the leeching process from those rocks will likely be reasonably slow. Although IANASC (I am not a soil chemist)

Kahawai--Are you in AZ? If so, your soil is probably alkaline and the iron wouldn't be readily available to them, anyway. In desert areas, it's more often a problem trying to get enough iron than having too much.

Second that.

Many red rocks and red soils only have a couple percent iron anyway, it just looks like more. It is not going to leach out of rock at any appreciable speed anyway. All soil is derived from weathered rock. Hey, if plants didn't grow around rocks there wouldn't be any plants.