I guess it comes down to Zookster's observation that Hulu doesn't offer the old broadcast shows in 5.1. That's not cool.
Then again, it seems like Netflix and/or Amazon wasn't offering 5.1 with the later Star Trek series last I checked. ST:Enterprise had respectable surround (I have them on my Hopper as I recorded them commercial free off HDNet).
I'm on a free month of commercial-free Hulu. After updating the app on my PS4, I'm getting 5.1 on everything I watch, including a recent movie, a Syfy TV series, and an A&E docuseries, in addition to Hulu originals.