They are. As Alex points out, a fair number are a mixture of single-reader many-writer or many-writer single-writer, and a few are many-writer many-reader.

MPMC: ck_stack, ck_fifo, ck_ring (in the works), ck_disruptor (pending push), ck_bitmap (but not linearized) and ck_hp*

And in some cases, these are just building blocks for more complex structures.

Specialized: - Everything else, including ck_[r]h{s,t}*.

The synchronization primitives are all generalized to multiple writers (exception is ck_swlock which is specialized). The manual pages should point out bounded concurrency.