as you already know its possible its gonna add flavor, if you dont mind lemon flavor in your beer i dont see why not, pretty much any acid can be used, some are dangerous so you wont see aqua regia, sulfuric or hydrochloric being used as far as i know unless you brew with fester Addams, i would not go near that stuff, i tried a few acids before phosphoric,lactic and citric powder, i dont personally like to complicate mash ph so i just use lactic now cause its predictable and a little goes a long way with minimal flavor contribution, all in all i don't think lemons will cause you problems its just diluted citric acid,absorbic acid, water and im sure a few other constituents