It would probably work fine, but without testing it in real life you’ll never know. I don’t believe anyone has tested whether or not the dual-core of the MBP can handle HD ProRes. Just make sure you have the option to return whatever you buy in case it doesn’t work out.
Having said that I think you are making a mistake. If you are working with HDV, you should capture and edit HDV natively. That is the superior workflow. And FCP 6 allows HDV footage that is not “cuts-only” to be rendered as ProRes. So it’s a lossless workflow.
EDIT: I just re-read the end of your post, I see you want live capture. So like I said, it will probably work but the only way to know for sure is to test it yourself.
Sean