I currently changed Hulu plans and no longer was grandfathered into my old plan, so now I can answer my question. Out of all the potential nightmarish scenarios that could occur, this was the one with the least problematic outcome since Hulu temp charged me for attempting to use my Roku device to add a Hulu Add-on. This doesn't mean that Hulu actually charged me but was instead testing my card to make sure it worked, much like when there's a free trial period -- at least I hope I don't receive a charge for doing this because I tried it twice to make sure it wasn't because of a time out issue, and I was temp charged twice for a total of $2.
So, the answer to question 4 is yes.
Perhaps I was unlucky, and I happened to try this on a day in which this service was glitchy, but I don't think that's it because you probably can't use Roku Pay for an Add-on if you're being billed through a provider's service that is not Roku.
I don't understand why Hulu allows me to attempt to use Roku Pay or even why they show their premium and partner Add-ons on the Hulu home page of my Roku device if I can't use Roku Pay to purchase any of them due to it erroring out.
Hulu--this feature just doesn't work: perhaps it never worked once Roku had to get involved by placing their Roku Pay with pin code on Hulu's app to stop anyone with the Roku remote from purchasing a Hulu Add-on without the account owner's permission. Hulu had recently added the feature of sending a link to the account owner's email to verify the identity before purchase, but the feature arrived years too late because with Roku's overlaying pay feature -- this didn't work for me as it once had before Roku Pay appeared. Since I was temp charged two dollars, this keeps me from making another attempt to try this on another day in the event this issue could potentially be fixed sometime in the future.
So, from this point on, we'll all assume that this feature doesn't work unless someone else decides to try this in the future -- you will be temp charged $1 for your effort so beware -- but seeing that no one has replied to this post in over six months, I'm just going to continue to assume that this feature doesn't work. Perhaps if you're using your Roku account to pay for Hulu, then this would work for you. This error could be happening because I'm using that new bundled service with Hulu which includes Disney+ and Max which could be the culprit -- who knows?
I was surprised, however, that it was Hulu that ran the temp charge instead of Roku, even though Roku required me to enter a credit card so I could complete the transaction on Roku Pay, so perhaps if it all worked, it would be Hulu that would have been the one to charge me for adding the Add-on through my Roku device instead of Roku.
I'm satisfied with this answer, and I will not attempt to use Roku Pay to add any Hulu Add-ons in the future; instead, I'll stick to using a web browser to add Hulu Add-ons through Hulu's website.
I found this to be such a hassle, that I've decided not to add that Hulu premium Add-on at this time, which would have been Cinemax since there are movies only on that channel that I would like to see, but I also want to watch many movies on other premium channels that I already subscribe too. So, Hulu -- enjoy that $2 temp charge instead of the amount you would have received had this feature worked. Maybe in a couple of months, I'll use your website to subscribe to that Cinemax Add-on.
Update: Hulu refunded both temp charges.
