At this time, there's no support for CUDA on QNX. The supported operating systems for CUDA are listed on the cuda download page as well as in section 1.4 of the release notes
Regarding Tegra, at this time there are no Tegra devices that support CUDA. The list of CUDA-enabled GPUs is here. Whether using an x86/x86_64 CPU or an ARM CPU, one of these CUDA GPUs is required for CUDA support.
Update: There are now tegra devices that support CUDA, including the widely available Tegra TK1 and recently announced TX1.