Placing a Quonset hut on a stem wall is not uncommon, but takes a little bit of planning ahead. In some cases your manufacturer can provide you with a foundation design for a relatively low stem wall. In some cases an engineer hired by you can design you a foundation that is more efficient in its use of concrete and rebar, versus a factory engineered stem wall design, such that the hiring of the engineer pays for itself.
One thing you have to realize about the structure of a Quonset hut and its foundation, which isn't immediately obvious, is that in addition to the gravitational force of the building pushing straight down on the foundation, the arched shape also exerts an outward, lateral thrust at its base. The slab foundation that is most commonly used with a Quonset hut is actually under tension, serving to tie the sides of the arch at the base, preventing the bottom of the arch from spreading or springing outward. Depending on the size of the hut, some of the factory foundation designs I have seen actually require quite a bit of extra rebar in the slab, helping the concrete to compensate for this outward thrust.
In order for your engineer to be able to design your foundation properly, you will need to get "reactions" for your building from your manufacturer, in lieu of ordering your building with their standard foundation design. These reactions consist of a table of engineering data that is unique to your building, which your engineer will use to design the foundation to resist the outward thrust and meet all relevant safety codes. You need to make it clear to your salesperson that you will need reactions for a custom foundation. Typically, you will also want to make sure to order base plates with the building, since the alternative to base plates, the "keyway foundation", isn't really suited to a stem wall setup.
It will definitely be less expense and trouble to just go with a standard foundation design if at all possible. But if for whatever reason you need to go with a custom foundation design, such as setting the building up a bit and/or allowing for a crawlspace underneath a wood framed floor, it is definitely doable, as long as you get the reactions and get a qualified local engineer on your team. Another scenario is a sloping site, where it might be simpler to pour side walls to set your Quonset hut upon, rather than grading/retaining a large area in order to do a more conventional slab foundation.