No, nobody else uses Roadmaster, which is actually part of Navistar RV (parent of Monaco and HR). When the old Monaco RV was still building beaver and Safari models, they were also on the Roadmaster chassis, but on other manufacturer ever used it.
The other major RV chassis builders are Freightliner and Spartan, and Tiffin builds its own chassis (from industry standard components) for some models. None of these are technically similar in design to the main Roadmaster concept, which uses a floating subframe with multiple air bags. However, the low end R4R Roadmaster is fairly similar to the low-end Freightliner XCS chassis. Thelatest Roadmaster chassis also uses Navistar engines, while Spartan and Freightliner use Cummins (or Detroit on a few high end models).
Other than the subframe thing, all the major RV chassis are fairly similar at a high level: air suspension, air brakes, solid axle or IFS, Allison transmissions and mostly all Cummins engines. You will also see some Cat and Mercedes engines from a few years ago, around 2005-2007.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL