Can greasy heel be located on the front of the rear fetlock joints?

Usually Greasy Heel affects the rear of the pasterns, but it can also affect the sides of the pasterns, so I don't see any reason why it can't affect the fronts of the fetlocks. But it may also be some other type of skin problem and if there is little improvement after using the greasy heel treatment, you should get the vet to come check him out.

"Grease heel" can affect any portion of any of a horse's legs, Donna. It's more commonly seen on the backs of the legs, just above the hooves, but it can also appear behind the knees, on the hocks, or even on the elbows of the horse.

Yes indeed.

Yup, it can also be at the backs of the knees.