Wow, I am so sorry you and Ollie had to go through this! How scary
We are regulars and I am on the board for our local dog park, but we just visit the small dog side. I would definitely avoid going to your dog park again if there is not a section separate from the large dogs for your pup to play. It is just not safe... You don't know what type of people and dogs are there, and with the size difference, you may not be so lucky next time.
I am so glad to hear that Ollie is going to be okay. Keep us updated on the case!