I have always measured seperately. I use about 1.8 oz priming for the 25 bottles and 1/4 cup for the party pig. I have had great results. I don't have room to get a real keg set up going, so the party pig works great for me. Keeps pressure to for at least 3 weeks...don't know after that since my batch is usually gone. (since then i have had pigs longer. I have had pigs keep carbonation for up to 4 months without a problem).
I wouldn't recommend priming the whole batch and then filling pig and bottles. I am only guessing, but based on what I have read on the party pig it doesn't take much to end up with "nothin' but foam"
Reason: addition of information