User always get a compilation success under emulator mode with vectorize kernel with channel, however the compilation fails with FGPA compilation mode. According to the OpeCL programming guide, it states that user cannot vectorize channels.
Intel Software: Intel FPGA SDK for OpenCL
There is a compiler bug that during emulator mode suppose to flag an warning when ever detect any vectorize kernel operation, so the compilation result should be tally with FGPA mode which is an compilation errror. A compilation fix/warning under emulator mode will be deployed in 18.0 SDK release.