Each channel provider controls and manages all content formatting and delivery within their channel, and will always be the best point of contact for any questions.
As you suggested, on 1/9/20 I posted the issue of no Hulu surround on Roku to the Hulu forum. I pointed out that the Hulu 5.1 announcement of 12/12/19 ( hulu.tv/SoundQuality ), as I mentioned above, said that 5.1 was supported by Hulu on "select models" of Roku. I asked if my model (Roku3 4200) was one of the select models.
I didn't get a reply, but I did notice that Hulu updated their 5.1 announcement today (1/10/20) to now say "Roku and Roku Stick (3810X, 3920X, 4400X and 46*0X models)" instead of the generic "Roku and Roku Stick (select models)". So I guess that means that Hulu does not support 5.1 on my Roku3.
Can you confirm that If I purchase one of the Roku models listed above that I will get 5.1 from Hulu?