It's something that you would have to test, unfortunately.
I know we had one successful import from Photopost Pro 5.5.6 a while ago. I had to make some code changes to get it to work. But I would definitely use it tentatively, and preferably only under test conditions in the first place.
The import seems to have went well. Updating counters and rebuilding search now. No errors and everything imported correctly. The media counts are off as is forum counts. After rebuilding everything should be good.
Now that test worked it's time to do it again on the live site.