You are probably right if you are focusing mainly on the big tools. You are wrong if you are open to looking at more modest tools that may be more applicable to your kind of environment. You are more likely to find what you want in Open Source (SourceForge.Net) in terms of smaller application test tools. Case tools are an overkill if you are dealing with predictable interfaces such as you find in control computing. The test tools you are aiming at should intercept the signals used by an interface and how you do that depends on your SDK tools. Since you do not tell us much I cannot say much more than that.
Actually, what YOU need to focus on is the coding that is required. I do not know what QNX supports and how well that is covered in Open Source tools but even if you have a custom language like TAL (Tandem, reminds you of C) you can use the basic design of JUnit and implement it in the language supported on your system. That is the beauty of Open Source.