Even if we assume there IS a linker, as you said: the emulator HAS the sources. AS ARE POINTED TO in the .abs file.

If the compiler/assembler managed to figure out where the include file is and what does it contain, the emulator software ultimately can do the same.
The emulator relies on the compiler/linker informing it about source file name and path. Were it to 'figure it out' by itself, that would require that the algorithm for ALL compiler/linker toolsets for finding files were the same.

It's the emulator maker who wants to make the deal: to sell the emulator.

If I know his emulator IS flawed, I don't care HOW and WHY. I will go to the competition and ask, how do their emulators handle includes in assembler - and decide accordingly.
ONE LAST TIME: the emulator is NOT 'flawed' the information provided to it is incomplete.

if this were to be worked out for the compiler/linker you happen to have and the emulator you happen to have, with a software upgrade to both, sure. Now be a relist, do you REALLY think that a compiler/linker maker would make a change that would make every emulator owned by its customers not function? I tell you that out Keil annual renewals (yes, we have more than one licence) would be cancelled immediately

Erik