While I don't have any inside info as to the maint. operation at ANGC, I will share a couple of thoughts from the standpoint of a "turf guy". First, there most definitely is a bermudagrass foundation that the ryegrass seed is sown into each fall. I have quite a bit of overseeding experience from the desert and can tell you that virtually all outstanding winter overseeded playing surfaces have an exquisite bermudagrass surface below to provide a desirable level of cushion and resiliency. Furthermore, I was quite surprised when I attended The Masters in that the ryegrass overseeding rates appeared to be substantially less than what I was accustomed to in the southwest. My estimate was that ANGC was seeding in the 600-650 pound per acre range whereas many of the more famous (or infamous) desert facilities are upwards of 800-1,000 pounds. I think in some instances we have taken the "Masters" effect and allowed it to run amok in the greenkeeping profession.
Secondly, the putting surfaces are indeed bentgrass. Interestingly, some of the germplasm used to develop the new Penn varieties (e.g Penn A-1, A-2, A-4, G-1, and G-6) was selected from portions of the mature greens at ANGC that exhibited finer texture, improved heat tolerance, deeper rooting etc. I believe those greens were originally Penncross but, for lack of a better phrase, had genetically adapted to the climate, close mowing and general demands of a championship caliber maintenance regimen. Goes to show that it typically isn't the type of turf that determines the quality of a playing surface but the man (or woman) managing the details.