I visited RM in early 2003, and toured the course with Jim Porter, the Asst. Super at the time. He told me the greens were the Sutton mix Mark Guiniven is talking about, and everything else Mark says about grass there makes sense too, except I didn't see much Penncross in the greens.
When I pressed Mr. Porter for more information on the Sutton mix composition, he either couldn't or wouldn't say. The greens were terrifically true with good speed, however.
I've managed my share of Penncross, and the greens didn't look like that species. If I had to guess, I would have said some mixture of bent/Poa/fescue.
There is no chemical that I know about that is toxic to Poa and perfectly safe on bentgrass. With products like endothal, mentioned in the article, it's a question of tolerances. The bent may tolerate a slightly higher rate of the chemical than the Poa does. Applying this sort of thing is like playing with fire, the slightest mis-step and you're typing up your resume and packing up the house.
This isn't the first prominent course to lose the gamble to rid the greens of Poa. Remember a few years ago when Loch Lomonds greens were toast during the Solheim Cup? AS I heard it, that was the result of a program to rid the greens of
Poa using Round-up. Very dangerous.
I'm happily married to Poa, myself.