Yup, that is good advice although his friend could be madly in love with her and won't be able to see the wood for the trees. Love is blind and all that. It could even lead to friction in the friendship. The friend might turn round and say something like that "You're just jealous because I've got a pretty woman on my arm".

Personally I'd gamble and intervene. Something needs to be said and he'll be thankful one day hopefully.