Hi,
I started supporting centosplus kernels directly at ATrpms, e.g. all kmdls for C4 and C5 plus (latest) kernels are being built. I would call this service experimental still, as I had some feedback by some users, but not nearly enough to make any more serious announcement.
Also I'm missing the src.rpm for the centosplus kernel from 2.6.18-8.1.15. The binary packages are there, just not the src.rpm. Maybe that's not that usrgent, as there will probably be a -55 centosplus kernel soon, I guess.