Actually, your Grandmaster Artisan CAN craft the gear for Level 55 of any school. I found this out when I accidentally purchased an Ice School Hat recipe on my Life wizard. Lower levels they will have to make themselves, but you only need one Grandmaster per account.
You can craft for other schools! My Life is my only crafter and he has crafted full Balance and Death gear and is working on Fire gear now. The issue is the school specific treasure cards. Just make those with the required wizard and "trade" them over to your other wizards through a friend. Works like a charm!