On another thread there was a video of a float equipped airplane landing on the grass. It can be done, but do it often enough and eventually your luck'll run out.
Perhaps if you rely on "luck"! But probably no more so than landing a float plane on water or even a land plane on grass.
Landing float planes on grass has been done routinely for a long time. The changing of seasons in places like Canada and Alaska brings about the need to switch from floats to wheels/skis for a considerable number of operators every year. Landing on grass or even harder surfaces at an airport or other suitable location is often preferable to making the change at waters edge. (logistics and suitability of takeoff areas are considered)
While it may seem odd to those unfamiliar, many float plane operators consider it fairly normal ops provided the surface used is pre-determined to be suitable. No more a matter of luck than any other competently planned and executed operation performed by experienced pilots the world over.
westhawk