CS8900 Interface to NIOS II

I'm pretty sure that uCLinux doesn't care about or use Altera's HAL. It has its own drivers. Altera's HAL tries to simulate a filesystem, which is redundant in uCLinux, where you have a real filesystem (not to mention an entirely different driver model).

That said, when you say uCLinux has a driver for the CS8900, do you mean that there is support for the CS8900 under the Nios II/Avalon Bus architecture? I mention this because there are lots of drivers for the PC architecture that aren't compatible with the Avalon bus architecture. The easy way to find out is to configure a Linux kernel and see if there's an option for the CS8900.