In arch/x86/Kconfig of the kernel tree it says for CMDLINE:
Enter arguments here that should be compiled into the kernel
image and used at boot time. If the boot loader provides a
command line at boot time, it is appended to this string to
form the full kernel command line, when the system boots.
However, you can use the CONFIG_CMDLINE_OVERRIDE option to
change this behavior.
In most cases, the command line (whether built-in or provided
by the boot loader) should specify the device for the root
file system.
and for CMDLINE_OVERRIDE:
Set this option to 'Y' to have the kernel ignore the boot loader
command line, and use ONLY the built-in command line.
This is used to work around broken boot loaders. This should
be set to 'N' under normal conditions.
So both commandlines will probably be used. I don't think an initramfs will normally interfere with the kernel commandline. In any case you can make sure you got what you wanted with cat /proc/cmdline.