Probably not. Because it is parklike, people walk and job on the paths during the day. The folks on the hayride were very low key, so no behavior problems. It just seemed an odd thing to do in a cemetary, on Memorial Day.
I did some poking around on the net. Seems like most cemeteries don’t allow any food or drink. However, since you were saying that this cemetery has a lot of regular passers-by, and is setup more like a park, it may be thought of differently. Still is kinda odd, though. As long as those people know why the hotdog cart is there and what they are honoring, I think it’s ok. Hope people don’t throw trash off the side of the hay cart. I’d probably pick it up and throw it back at them.