The MAAB check, jc_0201: Usable characters for Subsystem names, checks that the names of all Subsystem blocks conform to the constraints outlined in the link below:
https://www.mathworks.com/help/simulink/mdl_gd/maab/jc_0201usablecharactersforsubsystemnames.html
Subsystem block names are only checked if they appear in the generated C code. Therefore, the check excludes virtual and atomic subsystems with RTWSystemCode set to inline.