Possibly? But you really should have posted which video card you are using. Lacking that I'll assume you have a 5x70 card. With these card, to support three monitors there are some rules you need to follow. Read the following:
Mac Pro (Early 2009), Mac Pro (Mid 2010): Supported display configurations
Mac Pro (Mid 2010), Mac Pro (Early 2009): Issues with three displays and multiple DVI, HDMI connections
The general gist of these articles is that you need two active adapters to run thee monitors on 5x70 cards.
Here's a good explanation of what's going in here and why you need two active adapters on these cards:
Active vs. Passive Displayport adapters *the truth*
Your problem is there are no active adapters that I know of for HDMI connections. And this problem is compounded by the fact that you need dual link DVI to drive the 30" monitor.
I can see one possibility (not exactly that cheap). You could put the 30" on a mini-displayport to dual link DVI adapter. That would satisfy one of the active adapter requirements. Then you could use the following,
DVI & S/PDIF Digital Coax/Optical Toslink Audio to HDMI® Converter
That would satify the second active adapter requirement. I know it does because I use one of these for my TV (I also attach the S/PDIF into it to pump video/audio to the TV).