So after hours of heartache and trashed vinyl, I finally consulted with US cutter on an issue of my 721 stopping in the middle of a job. It kept throwing a communication failure error.
I'm using a MacBook Pro OSX 10.5.8, Illustrator, Signcut X2 and a MH 721 cutter. I was using this via USB. DON'T DO THIS!!!
US Cutter said to purchase a Keyspan USB to serial device. I couldn't find that brand specifically, so I bought an I/O Gear USB to Serial. Worked perfectly!
DO NOT BUY A BELKIN CONVERTER! The box says that it is Mac compatible, but it does not support OSX. I tried to install it, but it is written in Classic OS, not OSX. I was lucky that Staples took it back.
So in summary, yes, your setup would work and I'd be happy to let you know of any complications I had and resolutions. Just let me know...