I replaced the GPL code in the CloudFlare zlib with the BSD-like code from the Chromium browser. The pull request was just accepted, so you can now use CloudFlare zlib in place of the default zlib and it is faster on x86-64 and ARM CPUs. Those examples show the benefits for parallel workloads, but they are also present when used as a serial library.
My tests also show that zlib-ng falls between CloudFlare and default zlib in terms of compression speed, but it is faster for decompression. My validation did reveal a bug in the zlib-ng level 1 support, but it looks like patches are being reviewed.
Finally, @ningfei and I have submitted a pull request to pigz that provides Cmake support and supports non Latin characters for Windows. From previous comments I get the feel that the VTK developers do not want to use pigz. Therefore, the more relevant part of that pull request is the simple mechanism for selecting between zlib variants in the CMake script. Our project shows how the project can be built to target a preferred version of zlib (e.g. the system zlib, CloudFlare zlib, or zlib-ng). So that might provide a nice template where you can support the faster CloudFlare zlib now, and then seamlessly move to zlib-ng as it matures.