i don't think it is.. but i'll let someone else think up some examples with John..

certainly in italian, there are names like "Michaelathony" that are double name.. the second half does not get a capital. and for girls, Marygrace. (some one will be kind enough to provide the proper italian spelling, i am sure)

and in english-- the femine version of John, (Joan) can also be a double name.. Joanne.

i suspect johnathan is double name.. John Nathan run together, the only one i can think of for a man's name is the Francisxavier is sometimes run together..

but as Angel pointed out.. every one is creative-- even if they only express it in creating a name.