"I have to call you on that one. There is no IRS/IRU/ADIRU that updates from any external source...in any civil aircraft, be it Honeywell, Litton, etc. The FMC (FMS) will up date from GPS/DME/LOC/VOR."
Many years ago (pre-FMC), we had direct DME inputs to our 747 Classic INU's. Note that INU's are different from IRU's in that INU's have full navigation capabilities. IRU's require FMC's.
However, I guess you could argue the definition of "updating". During DME updating on our Classic 747's, DME-only position is used for navigation (not the inertial position), although the two values are compared for reasonableness inside the INU. You could say that the DME is not really modifying the basic inertial position, but the INU itself is outputting more accurate (DME) data.
This system was very labour intensive and involved manually inserting DME station info via the CDU.
Rgds.
NSEU