The suspension turned permanent, but it was much more complex than the NY Times made it out to be in early February of 1957, Dern's junior year. Doherty mentioned the sideburns (hair length wasn't an issue) as one thing of about 30. But the key was that Dern was split in his extra-curricular commitments between track and acting.
At the same time he was going to school, Dern was also attending classes at Philadelphia's American Foundation of Dramatic Art and had already appeared off-Broadway in "East of Eden." Within the year, he dropped out of Penn to study acting full time at the Actors' Studio in New York, and in 1958 was receiving strong reviews on Broadway.
It's important to spell out what may appear to be a minor distinction; Dern wasn't really kicked off, he resigned after being given an ultimatum. Minor, yes, but still important for the fuller view of what happened.
My sense from talking with Doherty about this was he was trying to get Dern to make some real choices and thought a hard-assed approach would help him see options with greater clarity. To some degree that may have been revisionist history on Ken's part as this was a conversation from about 20 years later. On the other hand, by the time I knew Doherty well I had longer hair and sideburns (that touched!) than Dern ever had, and I never sensed that this had any effect on our friendship.
Doherty was very much a cold warrior, set in his views of the world, particularly his thoughts on the glory of amateurism. At the same time that he thought track at its best was an amateur sport, he meant that in the sense of it being a recreation and pastime. But he maintained a love of dedication to a goal and a passion for the effort required to achieve that goal. In that sense, he was all for that aspect of professionalism as much as anyone.
I think what Doherty was trying to get out of Dern was a full commitment to something. Regardless of whether it was track or acting, Doherty was trying to get Dern to commit to making one of them a passion instead of being half-hearted about both.