Many assemblers allow file inclusion through "include 'filename'" type directives. It is conceivable that if more elaborate preprocessing is needed that can be arranged for, as well.
However, what you specifically ask for, including C header files in assembly files does not make sense. The result of preprocessing should be assembleable source code. Therefore, if the "C header" files contained simply #define directives, you are simply asking for token substitutions and that is reasonable. If, however, you try to include, say, a C function prototype declaration, that would be seen as invalid syntax from the point of view of an assembler.
