It looks like "Denver Mattress" is a Lippert Controls brand.
If you look at this page you'll see all the things Lippert makes for the RV industry - it's probably about 1/2 your RV.
If you back up to the Lippert Components the leading OEM and Aftermarket RV Parts and Accessory Supplier
page you'll find they make stuff for the Trucking industry, marine industry, home construction and much more.
There is no way this company makes all this stuff themselves. I bet them make a lot of the metal stuff (hitches, slideouts, etc.) and also the electronics (slideout controllers) since electronics appears to be where they started.
But most of this stuff is simply contract manufacturing.
Lippert has a great relationship with the RV industry - and when they see a need (like for a cheap mattress) - they go find a manufacturer, have it made and fill the need.
I don't doubt that they change their contract manufacturers as needed to cut cost or resolve objections from their customers (who is Jayco - not us).
Sounds like someone just left the original manufacturer's label's on the mattress Roosevelt.
But I don't think using contract manufacturers is deceptive - hell most of the stuff in your TV is made by a contract manufacturer working for Ford/Chevy/Dodge. In fact its frequently the same company - aka the airbag disaster from Tennaka.
That said - I'm glad to see that Jayco is using a real brand name mattress in many of their 2017 units - Simmons.