Though inertial altitude is liekly calculated continuously in the IRS, I have never seen any reference to the use of "inertial altitude" in any 744 documentation.
It is possible inertial altitude is used as a feed for the IVSI, but I am not certain. In a previous airplane, inertial altitude was used to "smooth" calculations of instantaneous altitude and V/S (to overcome pitot system lag), but were not accurate enough as a sole source.
ADC is still the most accurate and consistent source of altitude information for RNP purposes, though GPS and/or inertial altitude might be used in some airplanes as crosscheck sources.