No, the ruling doesn't specify - at least not the legal holding portion of the case. The case uses the language (when speaking about his parents)...
His father and mother were persons of Chinese descent, and subjects of the Emperor of China; they were at the time of his birth domiciled residents of the United States, having previously established and still enjoying a permanent domicil and residence therein at San Francisco
Nowhere in the decision do the words "legal resident" appear. Why? Because the concept of legal or illegal resident had no meaning at the time of that decision. It wasn't until a year or two later, when Congress passed its first immigration law - its name escapes me, but it had something to do with Chinese train laborers. Up until that time, anyone in the country was in the country legally, unless of course they were they bearing arms under a foreign flag.
You couple Ark with Plyler v Doe, and it becomes pretty clear how the Supreme Court would rule, if a case with specific question of "birth-right citizenship for illegals" would rule. My guess it would be 5-4, with Kennedy joining the majority.
No, the ruling doesn't specify - at least not the legal holding portion of the decision
In that case, the parents were NOT here in violation of US law.
One cannot as a matter of logic or legal analysis state as a conclusion that Wong Kim Ark holds that parents who ARE here in violation of US law are also "subject to the jurisdiction thereof" for purposes of the Fourteenth Amendment.
And the fact that Congress at the time of Wong Kim Ark had not yet decided to adopt legal prohibitions on foreign nationals residing in the U.S. makes the case even LESS relevant to the question of what "subject to the jurisdiction thereof" means for foreign nationals here in violation of U.S. law. The facts are simply inapposite to our question.