There's a lot of subtlety around this subject, and system-to-system variability, and it's not clear from the question why it's desirable to boot DOS from a computer set to UEFI-mode booting. This makes a practical answer difficult, but I can elaborate on some of the theory, and answer based on speculation about the true purpose of the question....
Most modern computers (most of those sold in the last 12 years or so) have Extensible Firmware Interface (EFI) or Unified EFI (UEFI) firmware. (I'll use "EFI" for simplicity.) Most, but not all, EFI implementations for x86/x86-64 CPUs have a component called the Compatibility Support Module (CSM), which enables them to boot older BIOS-mode OSes. CSM-enabled EFIs typically have a setup option to enable or disable the CSM (sometimes referred to by another term, such as "BIOS support" or "legacy mode"); however, precisely how that option works varies significantly from one computer to another. Usually, disabling the CSM in the firmware does just that -- it completely disables the CSM, so that you can't launch BIOS-mode OSes. On some implementations, though, "disabling" the CSM just drops its boot priority down below that of EFI-mode boot options. On such computers, "disabling" the CSM is more of a suggestion than a prohibition -- if the computer can't find any valid EFI-mode boot options, it'll try the BIOS-mode boot options, too. Some computers phrase their CSM option as if the computer will boot only BIOS-mode OSes if the CSM is enabled and only EFI-mode OSes if the CSM is disabled; but this is rarely true. In most cases, the ability to boot EFI-mode OSes is always active. Thus, the most accurate answer to the question, as stated is, "it depends" -- it might be possible to boot a BIOS-mode OS even with the CSM disabled, depending on the computer in use and whether there are valid EFI boot options in the boot list.
Also, be aware that EFI-based computers have a built-in boot manager to prioritize boot options. You might have installed two OSes, each of which creates its own boot entry; and the firmware may create additional boot options to enable booting removable media, boot from the network, etc. The CSM's BIOS-mode boot options are likely to be among these boot options (although they're a bit of a special case). Enabling or disabling the CSM can therefore change the set of boot options. This might not matter in some cases; if a valid EFI-mode boot option is first in the list, then it'll boot by default whether or not the CSM is enabled.
That's all theoretical, though. Presumably, @Greg G. has some unstated practical problem to solve. I don't know what that is, but I'm guessing that the need is to dual-boot DOS with some other EFI-mode OS. Most EFIs with CSMs make this possible, but it's a bit awkward. After installing both OSes, the boot manager can be accessed by pressing a certain key (usually a function key) as the computer powers on, and either the EFI-mode OS (usually identified by name) or the BIOS-mode OS (usually identified by a disk device) can be selected. To work in this way, the CSM will probably have to be enabled, though; disabling the CSM usually hides the BIOS-mode boot option(s) in the boot manager.
This can be made a little bit easier with my rEFInd boot manager. rEFInd scans for boot options and presents a menu on boot, so you won't need to hit the special key on every boot. By default, though, rEFInd does not scan for BIOS-mode boot options except on Macs; you need to edit the refind.conf file, uncomment the scanfor option, and add hdbios to the list to make rEFInd present BIOS-bootable disk options. As with using the computer's built-in boot manager, the CSM must be active for this to work.
Note also that DOS, AFAIK, requires a disk that uses the Master Boot Record (MBR) partition table. Most EFI-mode OSes create a GUID Partition Table (GPT) by default, which DOS can't read. Thus, dual-booting a BIOS-mode and an EFI-mode OS is likely to require separate MBR and GPT disks; however, there are workarounds. An OS like Linux can boot in EFI mode from an MBR disk or in BIOS mode from a GPT disk. There's also an ugly and dangerous hack known as a hybrid MBR. This was most commonly employed on Intel-based Macs to enable them to dual-boot the EFI-mode macOS with older BIOS-mode versions of Windows. In theory, it could be used to dual-boot DOS with Linux or FreeBSD on a non-Apple PC, but it wouldn't be useful for a dual-boot of BIOS-mode DOS with EFI-mode Windows, since Windows treats a hybrid MBR disk as an MBR disk, and Windows won't install in EFI mode on an MBR disk. Also, as I've said, hybrid MBRs are dangerous, so I strongly recommend against their use in most cases. I'm mentioning them only for completeness and their theoretical interest. If you want to dual-boot DOS and Windows on a modern PC, going with a straight BIOS-mode install is probably simplest, although that will limit the size of the installation disk. (You can still use a big GPT disk to hold Windows data.)
In most cases, rather than dual-booting DOS and a newer OS, it's likely to be better to run DOS in a virtual environment, such as VMware or VirtualBox, inside the more modern OS. DOS was designed with much less powerful computers in mind, so it'll run just fine in a very modest virtual machine. Because a virtual machine includes its own virtual firmware, you can run a BIOS-mode DOS in a VM that runs in an EFI-mode OS. This approach bypasses a lot of dual-boot problems and makes switching between the OSes trivially easy -- just click the right window, rather than reboot the computer.
