Yes, it is. The pelvis and base of the spine are composed of a number of bones that, like in the skull, are fused together. The base of the spine (sacro-iliac joint) can be vulnerable to both forms of arthritis, osteo and rheumatoid.
I meant to add that hip deterioration is often mistaken for pelvic pain because the hip joint angles in toward the groin/pelvis at the top of the thigh bone. If you're having pain in the "leg crease" between your thigh and pelvis, that's your hip joint.
Thank you very much, very informative