Hey there - I'm not going to be much help to you....but I spent a week in Samoa with a mate who was living there. We toured around the main island (that Apia is on) and stayed in some of the most beautiful places....and there appeared to be a fair bit of rock around near the coast. But it's very dark recently volcanic-looking stuff and I think it's pretty soft (tho I'm no geologist!).
I did a bit of searching when I cam back to see if there is any climbing there but didn't come up with much. Will be interested to see how you go here cos it's a beautiful place and would be great to climb there too.