Can I use openCL to develop an FPGA Accelerator device for an mac application

The OpenCL PCI-E driver which is required to communicate with the FPGA when using OpenCL will very likely not compile on Mac. You can always try to modify and compile it manually, and it might or might not work in the end, but Altera/Intel does not officially support it.

Also you will need to compile your OpenCL host code against Altera's OpenCL runtime, so you will eventually need to install Altera's tools on your machine. They have added support for ICD driver recently, so it might be possible to compile the host cost with other OpenCL runtimes (AMD, Intel CPU runtime, Nvidia, etc.), but I was not successful when I tried to do it myself.