So do you get all the gathering professions and then what others?
Only one of the shammies in my current main team has any professions, and those are Enchanting and Jewel Crafting

Outside of that team, I have a herbalist and a miner so that I can gather my own materials if I want to, but I so rarely even bother that it's hardly worth it.

The only "must have" for a multiboxing team is somebody capable of disenchanting. Beyond that it really just depends on what you like to spend your time doing.

My team, for example, spends all its life in heroics or battlegrounds, so I'd never use the gathering professions in any case.