It all depends where you hunt, if you're hunting somewhere like RSA then you have a fairly small group of staff looking after you and the average tip would be around ZAR30-60 per member of camp staff and at least twice that for your tracker/skinner.
If you're hunting in a true wilderness area such as Tanzania then you will end up with a much larger group of staff. Maybe 15-20 guys, (most of these countries work in US$). Depending on what these workers do the average would be $20-30 per camp worker and around double per hunting staff such as driver, trackers etc. Tip in a true wilderness area can sometimes add up to over $800.....a lot of money.
Usually the client tips the staff directly, but it's a good idea to ask your PH as in some places how you tip is more important than how much you tip.
A good book to read about planning a hunt would be "The Safari Experience" by Craig Boddington.
I sent James a copy of our safari cost breakdowns and will be happy to send the same thing to you if you can let me have an e-mail address.