The comment type (/// vs. //* */) wouldn’t matter.
It is supposed to be supported according to this:
I can’t get it to work either. It is probably a bug. It may be a NSURLRequest sandboxing bug where it tries to work but is blocked. It is not in common use, so likely it broke and nobody noticed. You could file a bug with Apple.
This is a known issue (rdar://39360782). I narrowly missed the window of opportunity to update the markup reference before it became part of the archived documentation.