I am not too sure about this, But I don't think it is redundant. Because, In the last rule you give a specific interface ( ie, allow forward if pkts from eth1 ). So I think there should be a rule to allow pkts from ppp0.
Anyway nothing harm in some experimenting :-)? ( Try removing the 2nd rule and see if ppl can still go out. If you find I am wrong, pl. post back so that me too can learn