I noticed a change when you do help someone and defeat the boss, however it's a very little change. Reviving blue phantoms in general can change the character towards white, but it's very time consuming unless you have the resurrection spell and there's alot of blues around, it would be quicker to just kill a BP.
1 Black Phantom kill = 8 Blues resurrecting
So if you start with a neutral tendency, about 3 BP kills will bring it to pure white while it would take 24 blues to bring it that high.
In short, yes you can bring it higher by helping players but it will take longer.
