A lot of their work has not been accepted into the mainline linux kernel ... but it's hard for me to see how this is a problematic sort of "not really crediting or even acknowledging". If anything, it pushes people to go to the source, grsecurity itself, for their "hardened" kernels. It seems that grsec/pax do have a lot of recognition as a result.
Yes, the inventors and developers of these hardening techniques want to be praised and have their work immediately used as-is to save the world. But we don't all have to want the same thing, to have the same priorities. We don't all face the same threats, nor performance and feature requirements. If people want to make the various trade-offs in favor of a significantly more "hardened" kernel, they've been free to use grsecurity or openbsd for quite a while. No need to blame linux-mainline maintainers for the people who have not made that choice. There's really no unfair lock-in going on here...
Those measures are meant to protect user space, not the kernel.
Unfortunately, by not really crediting or even acknowledging this research (and also ignoring a lot of work thats been happening in academia on hardening commodity kernels and applications), the Linux kernel is a)playing catch up to other operating systems (instead of adapting newer techniques) and b) alienating researchers even further.