Yes. But it depends on what is expected. Usually QNX plays nice with bootloaders like grub or lilo as it brings it's own bootloader as well. With this it is possible to choose between booting QNX or anything else.
If one would like to choose between different boot images they have other possibilities. On QNX4 filesystems the files /.boot and /.altboot are boot images. .boot is the default bootimage and .altboot will be booted if ESC is pressed during boot.
On QNX6 filesystems it is even possible to put multiple bootimages into the directory /.boot/ and you will be prompted to choose which image should be used during the boot process.
NOTE:
This entry has been validated against the SDP version listed above. Use
caution when considering this advice for any other SDP version. For
supported releases, please reach out toQNX Technical Support if you have any questions/concerns.