I'm guessing if anyone knew the answer to this I'd have received a quick response, so I opened a ticket and asked the same question. The response was to call the offline sales team for this information, which I did. They didn't have an answer for me and sent me to technical support, who assured me that there is a ParallelsVirtualizationSDK for version 8.
Since I've always had a hard time finding the latest SDK downloads on the Parallels site, I asked for a specific link, and the person I spoke with spent some time looking, and like me, was unable to find it. He's promised to get the information to me by tomorrow, and I will try to remember to post the info here so it can be located with a search.