As a player, I pee in hedges quite often, I tend to drink too much water before a game. For me, I look about to see if there are kids around, if there is, I wouldn't dream of doing it. If the coast is clear and I've found somewhere discreet, I'd certainly un-wind it and release thy urine!
As a referee, I wouldn't do it regardless unless I was actually going to pee my pants!
If I got told by an assessor or someone similar that I "should have cautioned" a player for urinating in a hedge, so long as that player met my criteria (No kids around, discreet and he's not doing it in the vicinity of a toilet), I'd tell him he can keep his marks!
I wouldn't expect players within senior football to be urinating in hedges due to the fact they pull in crowds and family's are often hanging about. In grassroots and low-level leagues, some teams can barely get facilities with running water! Also, if you saw some of the toilets I've seen in the sheds down here in Pasty-land, you'd rather take your chances outside!