I don't think I would let this go either. If it was a spelling test and the words were correctly spelled then he deserves to be graded on that alone - UNLESS the teacher was specifically grading on word placement on the page, which I highly doubt.
I also agree that you should talk to your son and explain to him, in the best way possible, that he needs to conform to the mold that is expected and stop being so dawg-gone creative....at least in spelling. (Sort of kidding here, but that seems to be what our children have to do - conform, conform, conform!!!)
If you do decide to contact the teacher about this, I would try to be as diplomatic as possible. If the teacher is already frustrated with your son you surely wouldn't want to add salt to the wound.
Hopefully the school year is almost over and this didn't bring his grade down.
