So, realistically speaking, it's kind of a Lincecum and Aram for Zimmerman deal. The only thing that worries me is how you're going to find 3B production until/if Aram returns to form. Looking at your offense, however, it seems as if you can gut that wait out with some thrifty matchups and such. If Aram starts to produce again, you would then not be losing much production out of that three hole by giving up Zimmerman. Lincecum is definitely worth that.
I know I'm not even considering Rivera, but it doesn't sound like you are either. I'd take the deal and strive for league average production out of your 3B slot until ARam gives you closure (one way or the other...)