I do accept her as a credible source. So let's look at exactly what she said:
'Sour and cynical...carping' Yes, I can believe all that.
'Insistence on inserting himself into other people's affairs' That's his comments about Ellsbury. I'd agree that the comments were ill-advised. Did they affect Ellsbury? I can't see how, considering he had an MVP-calibre season.
'turned him into a detriment' That's a pretty non-specific statement.
You can put your own interpretation on how harsh of a criticism this was on Youkilis. It certainly doesn't sound to me like anything comparable to a Manny situation.
As for what his teammates said, I'm sure if nobody had said anything, people would take that as a sign that the players didn't support him.