It's just impossible for me to imagine that they'd add unique Pokemon for the most expensive form of media and not give access to the general public.
Now if you mean something like using the park's Pokemon land as an introduction for some new next generation Pokemon a couple weeks or months before a game is released as
@jrn14 is saying, that sounds fine. But I'd be shocked if there were "park exclusive Pokemon"... that doesn't sound fair to the general public.