If you have characters with the Island items from both Horde and Alliance, you can use them on either faction, most items have different itemid/buffid so they do stack. I am using this primarily with Sun Stone - Spell - World of Warcraft and Lightprism - Item - World of Warcraft, I am alliance and the Sunstone damage is reduced but it's worth a bit of DPS. https://i.imgur.com/o8SEQ6P.png