For clarity, every variable I define globally in vibe.d is the same as thread-safe, correct? Basically, in regards to vibe.d, terms can mostly be used interchangeably? (With the exception of initializing with __gshared.)

I'm not sure if I said that right. I suppose, for a variable to be global, it must be full of static and const anyways. So, for a variable to be properly global, it must also be thread-safe (although I'm sure there are exceptions/mistakes that can be made). The two goals align.