Well, the first thing you should understand when looking into source ports is that there are different classifications. The most basic is Chocolate Doom, which aims to be exactly like the original game with all of its limitations and bugs, just made to work on modern operating systems. When someone refers to "vanilla compatible" they are referring to a map that could run on Chocolate Doom or even the original Doom executable. By extension this also means any vanilla compatible map can run with any other source port.