I wouldn't necessarily call this "support" because DOS itself does nothing for or against; and "all" you need to do conceptually is tickle the APIC to get the other cores running, something that can be done easily even in flat real mode (but this sample appears to use DPMI, so protected mode --- and DPMI itself begins to contain the elements of an OS.)

Not surprised to see the German comments; a lot of low-level PC stuff came from there in the 80s and 90s.