I don't know the specific purpose intended by that knurling, nor have I looked at a crank or rope seal that closely, but I just had an unrelated discussion with an oil expert about the fine details of different blends of ATF, so I'm inspired to throw in my .02:

Here's my assessment.

A lip seal will ride on a thin oil film on a journal. That film actually does the sealing during rotation while protecting the lip of the seal. If that boundary film can escape, though, oil will begin to seep out. So add some pumping grooves (the knurling) so that crankshaft rotation keeps the oil film in place (picture waves that keep a floating object near the shore).

I suspect a rope seal is more porous and allows the oil to penetrate it, which then swells it against its sealing surface, and it is kept cool at the rotating boundary by the absorbed oil (which is continuously refreshed to some extent by oil splash). I'm guessing that it has a different boundary layer, perhaps one that is a very tight matrix that prevents the oil molecules from escaping to an extent that would manifest into a user-noticeable amount (aka 'a leak').

Or maybe I'm completely FOS.