The MOVC instruction reads data from the Code address space - which is where ROMs are usually placed.
However, there is nothing to stop you placing ROM in the Data address space - just so long as you remember not to try to write to it!

You didn't say what language you're using; Keil's 8051-specific extensions in C51 provide keywords for explicitly accessing the different address spaces (CODE, XDATA, etc), locating variables at specific addresses, and macros for directly addressing absolute addresses.