Technically, any computing device can emulate any other, so the Zaurus (various models) could emulate others - but the limitations are storage and processing speed. With a big enough CF or SD card, storage need not be a problem, but the low processing speed limits the complexity of the emulation - plus, you'd be emulating the hardware as well. I doubt whether VirtualBox could run on a Z, but highly-optimised emulations - i.e. CPU emulation core written in ARM assembler - might work. UAE
runs quite well on my SL-5500, and it's written in C (note, I have not tried FS-UAE, but am using the old UAE).
I use the following rule: if the system to be emulated was made before 1990, it might work on the SL-5500. SIMH
works well because it is not too resource-hungry (apart from the VAX).