I personally wouldn't advise the chalice regardless of shared cooldown. Demo Aoe requires you to be in melee range of the adds, and if you have a tank like mine who likes to drag the adds around so that the boss gets hit by the aoe, having a static dps boost such as a well on the floor isn't very helpful. I have trouble seeing the lightwell sometimes, I don't know how you're going to manage benefiting from the full duration of the chalice.
Edit - You're better off using the one from V&T and if you don't have that I'd even suggest the blue trinket from Lost City of Tol'vir, as those adds would be at 25% and you might get a proc randomly
, you'd definitely benefit from the mastery on it.