Can a Dragonfire Adept 1/Dragon Shaman 4 use the two breaths independently?
So on round one, he breathes fire for 2d6 acid (green DS), next round 1d6 fire (DfA), and keep doing it until this until the acid from Dragon Shaman recharges?
The supernatural ability breath weapon of a level 4 dragon shaman, in part, says
Just like a true dragon, once you breathe you must wait 1d4 rounds before you can use your breath weapon again. (Player's Handbook II 14)
And the supernatural ability breath weapon of the dragonfire adept, in part, says
At 1st level, you gain a breath weapon that you can use at will as a standard action. (Dragon Magic 25)
These two abilities are unique and separate. Thus, for example, a multiclassed dragon shaman 4/dragonfire adept 1 can use her dragon shaman breath weapon then, while waiting for it to recharge, use her dragonfire adept breath weapon.